Hydrologic Modeling Using SWAT: Test the Capacity of SWAT Model to Simulate the Hydrological Behavior of Watershed in Semi-Arid Climate

Introduction

Over the history of Earth development climate has known many changes, the end of the ice age 7000 years ago, marks the beginning of a new climate cycle (IPCC, 2007). Population growth and pollution combined withclimate change, are some of the main issues that decision makers face when managing the most important resource, which is water, especially in developing countries like Morocco, indeed the country has a complex climate variability characterized by a long period of drought, extreme evapotranspiration, and early or late rains (FalhiS.& al., 2016). The main sequels of these changes are; changes in precipitation patterns, excessive drought and heat waves, the hurricanes will become more devastating, and the sea level will rise 1-4 feet by 2100 (IPCC, 2013). Similar deviations will have a harmful impact on ecosystem balance generally, and human life specifically. According to the fifth report of the Intergovernmental Panel of Climate Changes (IPCC), a decrease of up to 20% in rainfall is predicted by the end of this century, and the increase in temperature is expected to reach 2.5 °C to 5.5 °C under the same scenarios (IPCC, 2015).

Not to mention the availability of water has decreased from 3500m³/person/the year 1960 to 1000m³/person/year in 2000, a drop of 420 m³/person/year in 2020 is predicted, and therefore the water demand will increase in the future (IPCC, 2014).

The three major sources of water pollution in Morocco are; municipal wastewater discharge, industrial effluents, and agricultural activities, urban area generate around 500 m³/year of wastewater, and it may reach 900 m³ in 2020. The high salinity and nitrate concentration affect the underground water, streams are generally contaminated by phosphorus, ammonia, organic matters, and high coliform counts. This polluted water is directly discharged to a natural water body, for example, Sebou watershed which constitutes 29% of Moroccan water resources is heavily polluted by nitrates, phosphorus and pesticide residues (EnnabliM. &al.,2017).

Even though Innaouene watershed presents an important hydric potential of the oriental part of Morocco, because of its geomorphological situation and its karstic reservoir, the basin faced a set of problems such as floods, drought and water quality.

In the last decay, a devastating flood caused important humans and materials damages, in 1973, a hydroelectric reservoir was built in order to manage water and mitigate the floods (OECD,2017). However, the area still suffers from several problems, which relay its socio-economic development.

In the other hand, Innaouene River’s tributariesareexposed to sewage and margins release. The sequels of such actions are not only limited in the river level, but they alsospread and may affect the groundwater, the reservoir (which is essentially used for irrigation), the neighboring area, and on sanitary and environmental field.

Moreover, the basin did not evade the impact of global climate change, this later present semi-arid climate that has two major phases; dry and humid, therefore, the hydrological cycle does not assure a complete water renewal since evaporation and evapotranspiration are limiting factors.

In order to help manager and decision makers to adopt the appropriate land management techniques, the study of the hydrological behavior and quantification of water resources is paramount. Hydrological models are important tools for managing and planning a sustainable use of water resource to meet various demands. According to this perspective, this chapter remains part of hydrologic simulation using the SWAT model, the study is axed as below;