Modelling Water Balance Using Remotely Sensed Data:Application to the Ibrahim River Basin, Lebanon
- Project leaders
- Ivan Portoghese, Talal Darwish
- LIBANO - CNRS-L - National Council for Scientific Research of Lebanon
- CNR/CNRS-L 2012-2013
- Earth and Environment
- Thematic area
- Earth system science and environmental technologies
- Status of the project
The general trend in hydrological science aims at merging Earth Observation techniques (EO) and water balance modelling. Hydrology is in fact inherently related to many EO applications in forestry, agriculture and land cover, since water is a vital component in each of these disciplines. Most hydrological processes are dynamic, not only between years, but also within and between seasons, and therefore require frequent observations. EO techniques offer a synoptic view of the spatial distribution and dynamics of hydrological phenomena, often unattainable by traditional ground surveys and mostly unreachable in the Mediterranean regions. This approach is sought as one of the most promising fields in water resources investigations particularly addressing the dynamic water balance evaluation at river basin scale. In practice, the assimilation of remotely sensed data in hydrologic models allows for improving water and energy balance predictions as demonstrated by several science papers of the last decade, due to the similar pixel size at which remote sensing information and distributed water balance modelling operate.
Particularly in the Mediterranean region, reliable evaluations of precipitation partitioning into the different water balance components are crucial for water resources evaluation and allocation. Both surface and groundwater are often over-exploited with poor understanding of the potential of the available resources. With this regard, Lebanon and southern Italy, beside geo-climatic similarities, share common worries about their water resources reliability and utmost future water scenarios related to the climate change and socio-economic transformations.
Lebanon, along the Eastern Mediterranean Basin, was described as the "water tower" of the Middle East region, since it is characterized by several water resources both on surface and subsurface. An average precipitation of about 1000 mm/yr -with snow covering almost more than 20% of its territory - feeds 12 permanent watercourses, a large number of springs, as well as a number of aquifers and subsurface water conduits (Shaban, 2011).
However, the current situation does not reflect this demonstration on the existing water resources in Lebanon. Water shortage events occur and the inhabitants are often accusing water supply problems. This is still attributed to the mismanagement in the water sector as a result of lacking in data availability and measuring instrumentations, which are required to evaluate the status quo on water resources. This situation is caused by a number of challenging factors affecting the Eastern Mediterranean region such as the changing climatic conditions and the dramatic population growth exceeding 2% per year.
Thus, the exploitation of water resources in Lebanon became widespread, and water started to be considered as a natural resources under depletion. This has been reflected by the lowering water supply in urban areas and irrigated lands, also causing deterioration of water quality of many sources. Such conditions are well pronounced in the coastal zone of Lebanon where more than 70% of population is located. Thus, the terrestrial and marine ecosystems have been obviously degraded.
Yet, studies on water balance are rare enough to provide a reliable picture of the different hydrologic components, including surface water and groundwater resources. Whilst, it is utmost important to develop water balance models for different water basins in Lebanon in order to clearly understand the major controlling elements for water resources.
This study entails a joint research effort among experts in different disciplines from Italy and Lebanon: IRSA-CNR and CIHEAM-MAIB (Mediterranean Agronomic Institute of Bari, namely Khadra Roula and Zaccaria Daniele), Italy; NCSR, Lebanon. It aims at utilizing innovative techniques for data collection and processing, as well as for simulation modelling to determine relevant terms of the water balance in the Ibrahim River Basin (IRB), a typical, coastal Lebanese watershed with a miscellany of anthropogenic and physical components.
The study aims at modelling the hydrologic data, which can be almost collected through EO applications. Data retrieved from moderate and high-resolution satellite imagery (Modis, Spot, Quickbird, etc.) will be of valuable support on the behaviour of terrain features, including water resources, vegetation cover, human interference, and many other land cover/ land use components.
Small-scale and large scale variation in water bulk within the watershed will be assessed, including land cover and land use, crop water demand, leaf area index (LAI), evapotranspiration, soil-water retention.
The types of information required by the joint-research project will be as follows:
1. Climatic data, with a special emphasis on rainfall and temperature.
2. Weather information from Tropical Rainfall Mapping Mission (TRMM), a remotely sensed data source.
3. Satellite imagery, with particular focus to Modis (daily data source), Spot (high-resolution, 2m).
4. Soil, crop and water flow information collected through in-situ investigations and ground-based data collection using field sensor coupled with information and communication tools (ICT) and instrumentations.
The expected deliverables from the project include:
1. Validation of water balance modeling tools and diagnostic analysis of the volumetric measures conducted in the selected area of study on surface flows and on groundwater resources.
2. Validation of tools for modeling water demand and water use at medium and small-scale levels under local conditions.
3. Development of thematic maps (1:50000) and analysis of satellite images for the major water balance components.
4. Analysis of current water allocation and water policies.
5. Impact assessment of land cover and land use changes on the renewable water resources.
6. Modeling water balance under likely scenarios of climate change.
7. Detailed report with a comprehensive discussion and recommendations
8. Final data dissemination through a joint workshop.
The main goal of the joint project is to evaluate and validate the different elements of the water cycle of IRB in a modeling scheme, showing different variables and their space-time dynamics.
It can be specified as follows:
1. Identifying the analytical parameters of surface and groundwater resources in the area of concern.
2. Validate simulation modeling tools and establishing the interrelation between surface water and groundwater (e.g. infiltration rate, water abstraction to evapotranspiration, etc)
3. Developing and validating an applicable model that can be used for the rest of Lebanese watersheds.
4. Identifying the relationship of water dynamics with respect to precipitation and temperature changes.
5. Assess of water demand and its evolution along the years under different water management scenarios.
Last update: 27/11/2021