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Abstract. This paper introduces and presents the Spatial Processes in HYdrology (SPHY) model (v2.0), its development background, its underlying concepts, and some example applications. SPHY has been developed with the explicit aim of simulating terrestrial hydrology on flexible scales, under various physiographical and hydroclimatic conditions, by integrating key components from existing and well-tested models. SPHY is a spatially distributed leaky bucket type of model, and is applied on a cell-by-cell basis. The model is written in the Python programming language using the PCRaster dynamic modeling framework. SPHY (i) integrates most hydrologic processes, (ii) has the flexibility to be applied in a wide range of hydrologic applications, and (iii) on various scales, and (iv) can easily be implemented. The most relevant hydrological processes that are integrated into the SPHY model are rainfall–runoff processes, cryosphere processes, evapotranspiration processes, the dynamic evolution of vegetation cover, lake/reservoir outflow, and the simulation of root-zone moisture contents. Studies in which the SPHY model was successfully applied and tested are described in this paper, including (i) real-time soil moisture predictions to support irrigation management in lowland areas, (ii) climate change impact studies in snow- and glacier-fed river basins, and (iii) operational flow forecasting in mountainous catchments.

Abstract. Changes in water resources availability can be expected as consequences of climate change, population growth, economic development and environmental considerations. A two-stage modeling approach is used to explore the impact of these changes in the Middle East and North Africa (MENA) region. An advanced, physically based, distributed, hydrological model is applied to determine the internal and external renewable water resources for the current situation and under future changes. Subsequently, a water allocation model is used to combine the renewable water resources with sectoral water demands. Results show that total demand in the region will increase to 393 km 3 yr −1 in 2050, while total water shortage will grow to 199 km 3 yr −1 in 2050 for the average climate change projection, an increase of 157 km 3 yr −1 . This increase in shortage is the combined impact of an increase in water demand by 50 % with a decrease in water supply by 12 %. Uncertainty, based on the output of the nine GCMs applied, reveals that expected water shortage ranges from 85 km 3 yr −1 to 283 km 3 yr −1 in 2050. The analysis shows that 22 % of the water shortage can be attributed to climate change and 78 % to changes in socioeconomic factors.

ABSTRACT:The Middle East and North Africa (MENA) region can be considered as the most water-scarce region of the world. The Intergovernmental Panel on Climate Change projects strong changes in climate across MENA, further exacerbating pressure on available water resources. The objective of this study is to undertake a climate change assessment for 22 MENA countries in order to quantify the problems these countries may encounter up to 2050. To evaluate climate change in MENA, nine global circulation models representing two future periods (2020-2030 and 2040-2050) were statistically downscaled and compared with a current climate, defined as the period 2000-2009. Besides precipitation only this study also focuses on change in water demand by vegetation reference evapotranspiration (ETref). It was found that for both future periods the annual precipitation sum will decrease for the majority of countries, with decreases of 15-20% for the latter period. For some countries, e.g. Djibouti and Yemen, an increase in annual precipitation of 15-20% was found. The annual ETref shows an increase for all countries for both future periods, with the strongest increases for the latter period. For the extreme situation, it was found that the minimum monthly and annual precipitation sum does not become smaller in the future climate. It in fact increases. In contrast, the maximum monthly and annual ETref increases for all countries. This indicates that projected changes in demand are likely to have a more adverse effect than changes in supply. Spatial analysis showed that the largest precipitation decreases are to be found in southern Egypt, Morocco, central and coastal Algeria, Tunisia, central Libya, Syria, and central and eastern Iran. A case study for Morocco revealed that the potential water deficit, which is already apparent for the current climate, becomes even larger for the future climate.

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