Interannual and interdecadal oscillations in hydrological variables: Sources and modeling of the persistence in the Elbe River Basin

Wenn man die Existenz von physikalischen Mechanismen ignoriert, die für die Struktur hydrologischer Zeitreihen verantwortlich sind, kann das zu falschen Schlussfolgerungen bzgl. des Vorhandenseins möglicher Gedächtnis (memory) -Effekte, d.h. von Persistenz, führen. Die hier vorgelegte Doktorarbeit spürt der niedrigfrequenten klimatischen Variabilität innerhalb den hydrologischen Zyklus nach und bietet auf dieser "Reise" neue Einsichten in die Transformation der charakteristischen Eigenschaften von Zeitreihen mit einem Langzeitgedächtnis. Diese Studie vereint statistische Methoden der Zeitreihenanalyse mit empirisch-basierten Modelltechniken, um operative Modelle zu entwickeln, die in der Lage sind (1) die Dynamik des Abflusses zu modellieren, (2) sein zukünftiges Verhalten zu prognostizieren und (3) die Abflusszeitreihen an unbeobachteten Stellen abzuschätzen. Als solches präsentiert die hier vorgelegte Dissertation eine ausführliche Untersuchung zu den Ursachen der niedrigfrequenten Variabilität von hydrologischen Zeitreihen im deutschen Teil des Elbe-Einzugsgebietes, den Folgen dieser Variabilität und den physikalisch basierten Reaktionen von Oberflächen- und Grundwassermodellen auf die niedrigfrequenten Niederschlags-Eingangsganglinien. Die Doktorarbeit gliedert sich wie folgt: In Kapitel 1 wird als Hintergrundinformation das Hurst Phänomen beschrieben und ein kurzer Rückblick auf diesbezügliche Studien gegeben. Das Kapitel 2 diskutiert den Einfluss der Präsenz von niedrigfrequenten periodischen Zeitreihen auf die Zuverlässigkeit verschiedener Hurst-Parameter-Schätztechniken. Kapitel 3 korreliert die niedrigfrequente Niederschlagsvariabilität mit dem Index der Nord-Atlantischen Ozillations (NAO). Kapitel 4-6 sind auf den deutschen Teil des Elbe-Einzugsgebietes fokussiert. So werden in Kapitel 4 die niedrigfrequenten Variabilitäten der unterschiedlichen hydro-meteorologischen Parameter untersucht und es werden Modelle beschrieben, die die Dynamik dieser Niedrigfrequenzen und deren zukünftiges Verhalten simulieren. Kapitel 5 diskutiert die mögliche Anwendung der Ergebnisse für die charakteristische Skalen und die Verfahren der Analyse der zeitlichen Variabilität auf praktische Fragestellungen im Wasserbau sowie auf die zeitliche Bestimmung des Gebiets-Abflusses an unbeobachteten Stellen. Kapitel 6 verfolgt die Spur der Niedrigfrequenzzyklen im Niederschlag durch die einzelnen Komponenten des hydrologischen Zyklus, nämlich dem Direktabfluss, dem Basisabfluss, der Grundwasserströmung und dem Gebiets-Abfluss durch empirische Modellierung. Die Schlussfolgerungen werden im Kapitel 7 präsentiert. In einem Anhang werden technische Einzelheiten zu den verwendeten statistischen Methoden und die entwickelten Software-Tools beschrieben.

Changes in amino acid enantiomers and microbial performance in soils from a subtropical mountain oasis in Oman abandoned for different periods

An important feature of maintaining the agricultural stability in millennia-old mountain oases of northern Oman is the temporary abandonment of terraces. To analyse the effects of a fallow period on soil microbial performance, i.e. microbial activity and microbial biomass, samples of eight terrace soils abandoned for different periods were collected in situ, assigned to four fallow age classes and incubated for 30 days in the laboratory after rewetting. The younger fallow age classes of 1 and 5 years were based on the records of the farmers’ recollections, the two older fallow age classes of 10–20 and 25–60 years according to the increase in the D -to- L ratio of valine and leucine enantiomers. The increase in these two ratios was in agreement with that of the D -to- L ratio of lysine. The strongest relationship was observed between the increase in the D -to- L ratio of lysine and the decrease in soil microbial biomass C. However, the most stringent coherence between the increase in fallow age and soil properties was revealed by the decreases in cumulative respiration and net N mineralisation rates with decreasing availability of substrate to soil microorganisms. During the 30-day incubation following rewetting, relative changes in microbial activity (respiration and net N mineralisation) and microbial biomass (C and N)indices were similar in the eight terrace soils on a fallow age-class-specific level, indicating that the same basic processes occurred in all of the sandy terrace soils investigated.

Field measurements of the CO2 evolution rate under different crops during an irrigation cycle in a mountain oasis of Oman

For millennia oasis agriculture has been the backbone of rural livelihood in the desertic Sultanate of Oman. However, little is known about the functioning of these oasis systems, in particular with respect to the C turnover. The objective was to determine the effects of crop, i.e. alfalfa, wheat and bare fallow on the CO2 evolution rate during an irrigation cycle in relation to changes in soil water content and soil temperature. The gravimetric soil water content decreased from initially 24% to approximately 16% within 7 days after irrigation. The mean CO2 evolution rates increased significantly in the order fallow (27.4 mg C m^−2 h^−1) < wheat (45.5 mg C m^−2 h^−1) < alfalfa (97.5 mg C m^−2 h^−1). It can be calculated from these data that the CO2 evolution rate of the alfalfa root system was nearly four times higher than the corresponding rate in the wheat root system. The decline in CO2 evolution rate, especially during the first 4 days after irrigation, was significantly related to the decline in the gravimetric water content, with r = 0.70. CO2 evolution rate and soil temperature at 5 cm depth were negatively correlated (r = -0.56,n = 261) due to increasing soil temperature with decreasing gravimetric water content.

Settlement history of a mountain oasis in Northern Oman

To unravel the settlement history of oases in northern Oman, data on topography, the agricultural setting, water and soil parameters and archaeological findings were collected in the Wadi Bani Awf with its head oasis Balad Seet. Data collection lasted from April 2000 to April 2003 and was based on the establishment of a 3D-georeferenced map of the oasis comprising all its major infrastructural and agronomic features. At today's Balad Seet, a total of 8.8 ha are planted to 2,800 date palms and 4.6 ha are divided into 385 small fields dedicated to wheat, barley, sorghum, oats, alfalfa, garlic, onion, lime and banana. Radiocarbon dating of charcoal in the lower part of the main terrace system determined its age to 911 ± 43 years. Monthly flow measurements of four major aflaj systems showed a total maximum flow of 32 m^3 h^-1 with the largest falaj contributing 78% of the total flow. During drought periods, average water flow decreased by 3% per month, however, with significant differences between the spring systems. The analysis of the tritium/^3helium ratio in the water led to an estimated water age of up to 10 years. In combination with the flow data, this provided insights into the elasticity of the spring flow over time. The use of the natural resources of the Wadi Bani Awf by a pastoral population started probably in the early 3rd millennium BC. The first permanent settlement might have been established at Balad Seet during the first part of the 1st millennium BC. Presumably it was initiated by settlers from al-Hamra, a village at the southern foot of the Hajar mountains. Given an abundant und stable flow of springs, even in periods of drought, the construction of Balad Seet's first irrigation systems may have occurred at this early time. The combination of topographic, agricultural, hydro-pedological and archaeological data allowed assessment of the carrying capacity of this oasis over the three millennia of its likely existence. The changing scarcity of land and water and the eventual optimisation of their use by different aflaj constructions have been major driving forces for the development and apparent relativeley stable existence of this oasis.

Drainage, salt leaching and physico-chemical properties of irrigated man-made terrace soils in a mountain oasis of northern Oman

Little is known about the sustainability of irrigated oasis agriculture in northern Oman. The objective of this study therefore was to examine which factors allowed agricultural productivity to be apparently maintained during the two millenia of a mountain oasis’ existence. Soil moisture and physico-chemical properties were measured in a typical flood-irrigated field sown to alfalfa (Medicago sativa L.). Particle size, organic (C_org) and inorganic carbon content, pH and electrical conductivity (EC)of the soil profile were analyzed at 0.15, 0.45 and 1.00 m. Saturated hydraulic conductivity and the soil’s apparent bulk density and water potential were determined from undisturbed samples at 0.05, 0.25 and 0.60 m. During irrigation cycles of 6–9 days, volumetric water contents ranged from 30% to 13%. A tracer experiment with potassium bromide revealed that 52–56% of the irrigation water was stored in the upper 0.4 m of the soil. The rest of the water moved further down the profile, thus providing the necessary drainage to avoid the build-up of toxic salt concentrations. Due to differences in pore size, plant-available water in the topsoil amounted to 18.7% compared to 13% and 13.5% at 0.25- and 0.60-m depth, respectively. The aggregate structure in the upper 1.0 m of the profile is likely preserved by concentrations of calcium carbonate (CaCO3) from 379 to 434 mg kg^-1 and C_org from 157 to 368 mg kg^-1 soil. The data indicate that the sustainability of this irrigated landuse system is due to high water quality with low sodium but high CaCO3 concentration, the elaborate terrace structure and water management which allows adequate drainage.

Agricultural, architectural and archaeological evidence for the role and ecological adaptation of a scattered mountain oasis in Oman

The recent discovery of the monumental 5000 years old tower tombs on top of the up to 1850 m high Shir plateau has raised numerous questions about the economic and infrastructural basis of the agro-pastoral-piscicultural society which likely has constructed them. The scattered oasis settlement of Maqta, situated just below the towers in a rugged desert environment has therefore been studied from 2001 to 2003 to understand its prehistoric and present role along the ancient trade route which connected the inner-Omani Sharqiya across the southern Hajar mountains with the ocean port of Tiwi. Maqta consists of a central area with 59 buildings and 12 scattered temporary settlements comprising a total of about 200 semi-nomadic inhabitants and next to 900 sheep and goats. The 22 small springs with a flow rate between 5 and 1212-l h^-1 are watering 16 terrace systems totaling 4.5 ha of which 2.9 ha are planted to date palms (Phoenix dactylifera L.), 0.4 ha to wheat landraces (Triticum durum and Triticum aestivum) during the cooler winter months, 0.4 are left fallow and 0.8 h are abandoned. During a pronounced drought period from 2001 to 2003, the springs’ flow rate declined between 38% and 72%. Most of the recent buildings of the central housing area were found empty or used as temporary stores by the agro-pastoral population watching their flocks on the surrounding dry mountains. There is no indication that there ever was a settlement older than the present one. A number of Hafit (3100–2700 BC) and Umm an-Nar (2700–2000 BC) tombs just above the central housing area and further along one of the trade routes to the coast are the only indication of an old pastoral landuse in Maqta territory where oasis agriculture may have entered only well after 1000 AD. With this little evidence of existence during the 3rd millennium BC, Maqta is unlikely to have played any major role favouring the construction of the nearby monumental Shir tower tombs other than providing water for herders and their flocks, early migrant traders or tower tomb constructors.

Nutrient cycling and field-based partial nutrient balances in two mountain oases of Oman

Little is known about nutrient fluxes as a criterion to assess the sustainability of traditional irrigation agriculture in eastern Arabia. In this study GIS-based field research on terraced cropland and groves of date palm (Phoenix dactylifera L.) was conducted over 2 years in two mountain oases of northern Oman to determine their role as hypothesized sinks for nitrogen (N), phosphorus (P) and potassium (K). At Balad Seet 55% of the 385 fields received annual inputs of 100–500 kg N ha^-1 and 26% received 500–1400 kg N ha^-1. No N was applied to 19% of the fields which were under fallow. Phosphorus was applied annually at 1–90 kg ha^-1 on 46% of the fields, whereas 27% received 90–210 kg ha^-1. No K was applied to 27% of the fields, 32% received 1–300 kg K ha^-1, and the remaining fields received up to 1400 kg ha^-1. At Maqta N-inputs were 61–277 kg ha^-1 in palm groves and 112–225 kg ha^-1 in wheat (Triticum spp.) fields, respective P inputs were 9–40 and 14–29 kg ha^-1, and K inputs were 98–421 and 113–227 kg ha^-1. For cropland, partial oasis balances (comprising inputs of manure, mineral fertilizers, N2-fixation and irrigation water, and outputs of harvested products) were similar for both oases, with per hectare surpluses of 131 kg N, 37 kg P, and 84 kg K at Balad Seet and of 136 kg N, 16 kg P and 66 kg K at Maqta. This was despite the fact that N2-fixation by alfalfa (Medicago sativa L.), estimated at up to 480 kg ha^-1 yr^-1 with an average total dry matter of 22 t ha^-1, contributed to the cropland N-balance only at the former site. Respective palm grove surpluses, in contrast were with 303 kg N, 38 kg P, and 173 kg K ha^-1 much higher at Balad Seet than with 84 kg N, 14 kg P, and 91 kg K ha^-1 at Maqta. The data show that both oases presently are large sinks for nutrients. Potential gaseous and leaching losses could at least partly be controlled by a decrease in nutrient input intensity and careful incorporation of manure.

Plant genetic diversity, irrigation and nutrient cycling in traditional mountain oases of northern Oman

Little is known about plant biodiversity, irrigation management and nutrient fluxes as criteria to assess the sustainability of traditional irrigation agriculture in eastern Arabia. Therefore interdisciplinary studies were conducted over 4 yrs on flood-irrigated fields dominated by wheat (Triticum spp.), alfalfa (Medicago sativa L.) and date palm (Phoenix dactylifera L.) in two mountain oases of northern Oman. In both oases wheat landraces consisted of varietal mixtures comprising T. aestivum and T. durum of which at least two botanical varieties were new to science. During irrigation cycles of 6-9 days on an alfalfa-planted soil, volumetric water contents ranged from 30-13%. For cropland, partial oasis balances (comprising inputs of manure, mineral fertilizers, N2-fixation and irrigation water, and outputs of harvested products) were similar for both oases, with per hectare annual surpluses of 131 kg N, 37 kg P and 84 kg K at Balad Seet and of 136 kg N, 16 kg P and 66 kg K at Maqta. Respective palm grove surpluses, in contrast were with 303 kg N, 38 kg P, and 173 kg K ha^-1 yr^-1 much higher at Balad Seet than with 84 kg N, 14 kg P and 91 kg K ha^-1 yr^-1 at Maqta. The results show that the sustainability of these irrigated landuse systems depends on a high quality of the irrigation water with low Na but high CaCO3, intensive recycling of manure and an elaborate terrace structure with a well tailored water management system that allows adequate drainage.

Carbon and nitrogen emissions from stored manure and cropped fields in irrigated mountain oases of Oman

Little is known about gaseous carbon (C) and nitrogen (N) emissions from traditional terrace agriculture in irrigated high mountain agroecosystems of the subtropics. In an effort towards filling this knowledge gap measurements of carbon dioxide (CO_2), methane (CH_4), ammonia (NH_3) and dinitrous oxide (N_2O) were taken with a mobile photoacoustic infrared multi-gas monitor on manure-filled PE-fibre storage bags and on flood-irrigated untilled and tilled fields in three mountain oases of the northen Omani Al Jabal al Akhdar mountains. During typical 9-11 day irrigation cycles of March, August and September 2006 soil volumetric moisture contents of fields dominated by fodder wheat, barley, oats and pomegranate ranged from 46-23%. While manure incorporation after application effectively reduced gaseous N losses, prolonged storage of manure in heaps or in PE-fibre bags caused large losses of C and N. Given the large irrigation-related turnover of organic C, sustainable agricultural productivity of oasis agriculture in Oman seems to require the integration of livestock which allows for several applications of manure per year at individual rates of 20 t dry matter ha^−1.

Matter fluxes in mountain oases of Al Jabal Al Akhdar, Oman

Since 1970 when Sultan Qaboos bin Said Al Said took over power from this father, agriculture in Oman has undergone major transformations as a consequence of rapid population and economic growth. In this process groundwater extraction has dramatically increased to meet domestic and agricultural needs. Recently, the agro-ecosystem of ancient mountain oases of Oman have received greater attention as interest has grown to understand the causes of their often millennia old sustainable productivity. Particularly little is known about the carbon (C) and nutrient turnover in these intensive landuse systems. This is partly due to the difficulties to measure such processes in the often remote fields. To fill the existing gap of knowledge, field studies were conducted in five oases at different altitudes of Al Jabal Al Akhdar, the highest agricultural area in Oman, to determine C and nutrient fluxes as well as nutrient use efficiencies for two different cropping systems as affected by temperature, irrigation, and manure quality. The results of this study indicated that water scarcity as a result of low precipitation and an increase in urban water consumption is a major threat to the sustainability of agriculture in these oases. Optimizing the use of irrigation water is a major challenge for agriculture in these oases, particularly given ever increasing competition for this most limiting resource. Traditionally, farmers of these oases adapt to variation of irrigation water supply by minimizing the growing area of annual crops, leaving these areas uncultivated through drought seasons (Luedeling and Buerkert 2008). In this study, a remarkable reduction in annual crop area was observed in 2009 for all oases. Our results suggested that water scarcity as a result of low precipitation and the increase in urban water consumption cause such changes in land use. The data also underline the intensive C and nutrient turnover in the man-made irrigated agroecosystems and confirmed the importance of the large manure quantities applied continuously to the terraces as a key factor responsible for sustainable soil productivity. To trace the fate of C and plant nutrients that are released from the large amount of manure applied by oasis farmers, more detailed studies under controlled conditions, using isotope signatures, would be needed.

Downscaling and Modeling the Effects of Climate Change on Hydrology and Water Resources in the Upper Blue Nile River Basin, Ethiopia

The Upper Blue Nile River Basin (UBNRB) located in the western part of Ethiopia, between 7° 45’ and 12° 45’N and 34° 05’ and 39° 45’E has a total area of 174962 km2 . More than 80% of the population in the basin is engaged in agricultural activities. Because of the particularly dry climate in the basin, likewise to most other regions of Ethiopia, the agricultural productivity depends to a very large extent on the occurrence of the seasonal rains. This situation makes agriculture highly vulnerable to the impact of potential climate hazards which are about to inflict Africa as a whole and Ethiopia in particular. To analyze these possible impacts of future climate change on the water resources in the UBNRB, in the first part of the thesis climate projection for precipitation, minimum and maximum temperatures in the basin, using downscaled predictors from three GCMs (ECHAM5, GFDL21 and CSIRO-MK3) under SRES scenarios A1B and A2 have been carried out. The two statistical downscaling models used are SDSM and LARS-WG, whereby SDSM is used to downscale ECHAM5-predictors alone and LARS-WG is applied in both mono-model mode with predictors from ECHAM5 and in multi-model mode with combined predictors from ECHAM5, GFDL21 and CSIRO-MK3. For the calibration/validation of the downscaled models, observed as well as NCEP climate data in the 1970 - 2000 reference period is used. The future projections are made for two time periods; 2046-2065 (2050s) and 2081-2100 (2090s). For the 2050s future time period the downscaled climate predictions indicate rise of 0.6°C to 2.7°C for the seasonal maximum temperatures Tmax, and of 0.5°C to 2.44°C for the minimum temperatures Tmin. Similarly, during the 2090s the seasonal Tmax increases by 0.9°C to 4.63°C and Tmin by 1°C to 4.6°C, whereby these increases are generally higher for the A2 than for the A1B scenario. For most sub-basins of the UBNRB, the predicted changes of Tmin are larger than those of Tmax. Meanwhile, for the precipitation, both downscaling tools predict large changes which, depending on the GCM employed, are such that the spring and summer seasons will be experiencing decreases between -36% to 1% and the autumn and winter seasons an increase of -8% to 126% for the two future time periods, regardless of the SRES scenario used. In the second part of the thesis the semi-distributed, physically based hydrologic model, SWAT (Soil Water Assessment Tool), is used to evaluate the impacts of the above-predicted future climate change on the hydrology and water resources of the UBNRB. Hereby the downscaled future predictors are used as input in the SWAT model to predict streamflow of the Upper Blue Nile as well as other relevant water resources parameter in the basin. Calibration and validation of the streamflow model is done again on 1970-2000 measured discharge at the outlet gage station Eldiem, whereby the most sensitive out the numerous “tuneable” calibration parameters in SWAT have been selected by means of a sophisticated sensitivity analysis. Consequently, a good calibration/validation model performance with a high NSE-coefficient of 0.89 is obtained. The results of the future simulations of streamflow in the basin, using both SDSM- and LARS-WG downscaled output in SWAT reveal a decline of -10% to -61% of the future Blue Nile streamflow, And, expectedly, these obviously adverse effects on the future UBNRB-water availibiliy are more exacerbated for the 2090’s than for the 2050’s, regardless of the SRES.

Effects of changing water availability on land use in irrigated mountain oases of Al Jabal Al Akhdar, northern Oman

In Oman, during the last three decades, agricultural water use and groundwater extraction has dramatically increased to meet the needs of a rapidly growing population and major changes in lifestyle. This has triggered agricultural land-use changes which have been poorly investigated. In view of this our study aimed at analysing patterns of shortterm land-use changes (2007-2009) in the five irrigated mountain oases of Ash Sharayjah, Al’Ayn, Al’Aqr, Qasha’ and Masayrat ar Ruwajah situated in the northern Oman Hajar mountains of Al Jabal Al Akhdar where competitive uses of irrigation water are particularly apparent. Comprehensive GIS-based field surveys were conducted over three years to record changes in terrace use in these five oases where farmers have traditionally adapted to rain-derived variations of irrigation water supply, e.g. by leaving agricultural terraces of annual crops uncultivated in drought years. Results show that the area occupied with field crops decreased in the dry years of 2008 and 2009 for all oases. In Ash Sharayjah, terrace areas grown with field crops declined from 4.7 ha (32.4 % of total terrace area) in 2007 to 3.1 ha (21.6 %) in 2008 and 3.0 ha (20.5 %) in 2009. Similarly, the area proportion of field crops shrunk in Al’Ayn, Qasha’ and Masayrat from 35.2, 36.3 and 49.6 % in 2007 to 19.8, 8.5 and 41.3 % in 2009, respectively. In Al’Aqr, the area of field crops slightly increased from 0.3 ha (17.0 %) in 2007 to 0.7 (39.1 %) in 2008, and decreased to 0.5 ha (28.8 %) in 2009. During the same period annual dry matter yields of the cash crop garlic in Ash Sharayjah increased from 16.3 t ha-1 in 2007 to 19.8 t ha-1 in 2008 and 18.3 t ha-1 in 2009, while the same crop yielded only 0.4, 1.6 and 1.1 t ha-1 in Masayrat. In 2009, the total estimated agricultural area of the new town of Sayh Qatanah above the five oases was around 13.5 ha. Our results suggest that scarcity of irrigation water as a result of low precipitation and increased irrigation and home water consumption in the new urban settlements above the five oases have led to major shifts in the land-use pattern and increasingly threaten the centuries-long tradition and drought-resilience of agriculture in the oases of the studied watershed.

Sustainability of Small Scale Farming in a Mountain Region: Case Study of the Khaling Rai Population of the Solukhumbu, Nepal

The Khaling Rai live in a remote area of the mountain region of Nepal. Subsistence farming is central to their livelihood strategy, the sustainability of which was examined in this study. The sustainable livelihood approach was identified as a suitable theoretical framework to analyse the assets of the Khaling Rai. A baseline study was conducted using indicators to assess the outcome of the livelihood strategies under the three pillars of sustainability – economic, social and environmental. Relationships between key factors were analysed. The outcome showed that farming fulfils their basic need of food security, with self-sufficiency in terms of seeds, organic fertilisers and tools. Agriculture is almost totally non-monitized: crops are grown mainly for household consumption. However, the crux faced by the Khaling Rai community is the need to develop high value cash crops in order to improve their livelihoods while at the same time maintaining food security. Institutional support in this regard was found to be lacking. At the same time there is declining soil fertility and an expanding population, which results in smaller land holdings. The capacity to absorb risk is inhibited by the small size of the resource base and access only to small local markets. A two-pronged approach is recommended. Firstly, the formation of agricultural cooperative associations in the area. Secondly, through them the selection of key personnel to be put forward for training in the adoption of improved low-cost technologies for staple crops and in the introduction of appropriate new cash crops.