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Ludwig-Maximilians-Universität München. (2012)

Uncertainty analysis of hydrological model results and assessment regarding water risks in the Mediterranean Basin – Case study : Chiba, Tunisia

Hummel, Franz Maximilian

Titre : Uncertainty analysis of hydrological model results and assessment regarding water risks in the Mediterranean Basin – Case study : Chiba, Tunisia

Auteur : Hummel, Franz Maximilian

Université de soutenance : Ludwig-Maximilians-Universität München.

Grade : Master 2012

Résumé partiel
Mediterranean countries are very vulnerable to possible impacts of climate induced changes on hydrological budgets and extreme events. Mediterranean regions are already affected by a variety of natural and man-made threats regarding water security like severe droughts, extreme flooding, salinization of coastal aquifers, degradation of fertile soils and increasing desertification due to unsustainable management practices. With climate change amplifying these problems in the future there would arise increased potential for tensions and conflicts in this area. Despite the scientific knowledge that these changes may occur it is difficult to quantify these changes due to a variety of inherent sources of uncertainty. That was enough reason for the European Commission (EC) to initialize a series of projects within the Seventh Framework Programme Collaborative Research Project (FP7). Therein the project CLIMB (Climate Induced Changes on the Hydrology of Mediterranean Basins - Reducing Uncertainty and Quantifying Risk through an Integrated Monitoring and Modeling System) was started which should investigate present and future climate induced changes in the hydrological budgets and extremes for Mediterranean and neighboring countries. This master thesis applies techniques to quantify uncertainties and associated risks in Chiba basin for a reference (1971 – 2000) and scenario period (2041 – 2070) respectively. The Chiba catchment is a test site of the CLIMB project and situated on Cap-Bon peninsula in the north east of Tunisia. Two studies form a series of 108 hydrological model simulations that are being performed with the hydrological model WaSiM-ETH. One is a parameter uncertainty study (PUS) that investigates the effects of applying a varying set of important model parameters on a constant climate data set. The other is a climate signal uncertainty study (CUS) to quantify the impact of using different climate data sets on one basic model parameterization. Evaluation of CUS and PUS enables to quantify uncertainties of key outputs of interest as well as to investigate how these values may change in the future. This is complemented by a sensitivity analysis (SA) to determine most important input factors for ’relative soil water content in the root zone’ and ’ground water recharge’. SA also enables an investigation whether uncertainties of those values can be further reduced. Besides that a feasibility study examines whether tomatoes can be cultivated in the watershed under future climate conditions (rainfed —> without irrigation). At last selected climate change and hydrological indices analyze developments regarding droughts and extreme events as well as water scarcity in the study area. Nowadays water scarcity already forces anthropogenic actions in Chiba basin like irrigation of agricultural land and overexploitation of Korba ground water aquifer. This facilitates a drop of ground water levels near the coast and thus sea water intrusion with deteriorating effects on water quality. Therefore quantifying climate induced changes on hydrological water budgets and extremes (e.g. droughts) is of great interest in this region. Findings of this study estimate annual mean values of surface air temperature in Chiba basin to rise by 1.8C +/- 0.1C between the reference and scenario period. Annual sums of rainfall indicate a decrease of 59.3 mm +/- 17.2 mm (-16.9 % +/- 4.9 %). This has further negative effects on relative soil water content in the root zone [-0.013 +/- 2.5E-03 (-14 % +/- 2.7 %)] as well as actual evapotranspiration [-40.4 mm +/- 7.9 mm (-12.5 % +/- 2.4 %)]. Climate induced changes in the water balance of Chiba basin amount to 3.33 million m3 (-66.1 %) of less available water (best estimate) on average and for every year. Precipitation constitutes the key output to worry within this study.


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