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Impact of climate and land use change on water resources, crop production and land degradation in a semi-arid area (using remote sensing, GIS and hydrological modeling)

dc.contributor.advisorKappas, Martin Prof. Dr.
dc.contributor.authorRafiei Emam, Ammar
dc.titleImpact of climate and land use change on water resources, crop production and land degradation in a semi-arid area (using remote sensing, GIS and hydrological modeling)de
dc.contributor.refereeGerold, Gerhard Prof. Dr.
dc.description.abstractengWater resources have become scarcer in semi-arid regions of Iran due to increasing water use and recurrent drought. Any change to the hydrological cycle may have significant effects on the fragile ecosystems of Iran’s arid and semi-arid regions. Moreover, it can lead to land degradation. Therefore, water resources should be considered quantitatively for better planning and management. The main goal of this research was the impact assessment of climate and land use change on water resources (e.g. groundwater recharge, surface runoff, soil water content, actual evapotranspiration), and crop production in the Razan-Ghahavand Basin (RGB) in the central drainage basin of Iran. To attain this goal the objectives were: to model the availability of water resources components in temporal and spatial aspects, to estimate groundwater recharge (as groundwater is the main source of the water supply in RGB), to model crop yields in irrigated and rain-fed lands, to assess the relationship between water balance fluxes and land degradation. And, finally, to compare the results of actual evapotranspiration estimated by a remotely sensed process and a hydrological model. The first step of the research was a detailed quantification of the water balance components (e.g. percolation, evapotranspiration, soil water) of the RGB by means of hydrological modeling. To do this, a SWAT (Soil and Water Assessment Tools) physically based and spatially distributed, and an eco-hydrological model was conducted. The model was calibrated by SUFI-2 algorithm in two steps: Firstly, the model was calibrated based on the monthly river discharge. Then the calibrated model was recalibrated again by annual crop yield. The calibration of crop yield leads to estimate the evapotranspiration term better, which consequently increased our knowledge of estimating other water fluxes such as aquifer recharge. The sensitive and uncertainty analyses were also applied to assess the model’s performance. The calibration period was from 1998 to 2001 and the validation period was from 2002-2008, both for river discharge and crop yield. The results were satisfactory for river basins and wheat yield in both calibration and validation periods. All water balance components were quantified at the sub basin level in monthly time intervals. As groundwater is the main water resource in the RGB, the groundwater recharge specifically was estimated and the relationship between groundwater recharge, water level, and land degradation was evaluated. The results showed that there was not any significant change in groundwater recharge during the period 1998-2008. Therefore, a net withdrawal of groundwater, especially for the purpose of irrigation, leads to land degradation (e.g. land subsidence) in the area. In the next step, an ensemble of four Global Circulation Models (GCMs) under a fourth assessment report (AR4) by the Intergovernmental Panel on Climate Change (IPCC) in three emission scenarios (e.g. A1B, A2, B1) for the period 2046-2065, were developed. The data was downscaled by the LARS-WG model in all rain gages and synoptic stations. All data were fed into the calibrated hydrological model to analyze the future effects of climate on water resources, and wheat yield in the RGB. Finally, we interpreted the relationship between climate change and land degradation across the RGB. The results showed a substantial reduction in groundwater recharge and surface runoff, while in the basin surface runoff increased. Furthermore, the results showed that urbanization increasingly leads to surface runoff and flooding in the area. Assessing the wheat yield both in irrigated and rain-fed lands, a reduction of yield could be shown in rain-fed land due to decreasing soil moisture and rainfall leading to increasing water stress. The results also revealed that the risk of drought in the south and flooding in the north is high. The results highlighted the risk of land degradation by groundwater deterioration, soil salinization, and land subsidence in the basin. Finally, the estimation of the remotely sensed process of evapotranspiration (i.e. surface energy balance method) was done by the SEBAL (Surface Energy Balance Algorithms for Land) method. The estimation of ETa by remote sensing is comparable to the estimation of ETa by the hydrological model. The idea behind this part of research was that, if the ETa estimated by the surface energy balance method (i.e. remote sensing process) was the same as estimated by the hydrological model, remotely sensed data could further be used to calibrate the hydrological models, especially in the area with low data availability. The results of this part showed the good relevance between monthly ETa estimated by remote sensing and ETa estimated by the hydrological
dc.contributor.coRefereeSchaldach, Rüdiger PD Dr.
dc.contributor.thirdRefereePörtge, Karl-Heinz Prof. Dr.
dc.contributor.thirdRefereePropastin, Pavel PD Dr.
dc.contributor.thirdRefereeErasmi, Stefan Dr.
dc.subject.engRemote Sensingde
dc.subject.engClimate Changede
dc.subject.engWater Resourcesde
dc.subject.engFood Securityde
dc.subject.engLand Degradationde
dc.affiliation.instituteFakultät für Geowissenschaften und Geographiede
dc.subject.gokfullHydrologie (PPN613605179)de

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