Ecosystem services & virtual water flows

Quantifying impacts on local ecosystem services

People depend on ecosystems and the services they provide, for example, the provision of water and food, disease management, and climate regulation. The benefits humans derive from ecosystems are called ecosystem services. Over the past 50 years, humans have changed ecosystems more rapidly and extensively to meet growing demands for food, fresh water, and energy.

The Soil and Water Assessment Tool (SWAT) is a small watershed to river basin-scale model that is used to simulate the quality and quantity of surface and groundwater. It predicts the environmental impacts of water use, land management practices, and climate change. Model results can be used to quantify ecosystem services, such as the provision of freshwater for municipal, industrial, and agricultural uses or instream flows that support fisheries, recreation, and hydropower generation. For the MedWater project, an eco-hydrological SWAT model is being created for the Western Mountain Aquifer (WMA) that also accounts for the aquifer’s karstic characteristics.

This model is based on a digital elevation model (Figure 1), soil type and land use maps (Figure 2) and climate data (rainfall, temperature, wind speed, relative humidity, and solar radiation). The watershed was divided into  112 subbasins, and the aquifer’s recharge zone was identified. Each subbasin was divided into hydrologic response units (HRU), which are the building blocks in a SWAT model. Each reflects a unique combination of soil, land cover, and slope attributes. Key parameters were modified to reflect the aquifer’s karstic features.

Figure 1: Digital elevation model of the Western Mountain Aquifer
Figure 2: Soil and land use classes used in the development of the SWAT model













Figure 3: Model results (uncalibrated) for annual precipitation, evapotranspiration and percolation from 1992 to 2012

An initial model has been run for the time period 1992 to 2012. This model still needs to be calibrated using stream discharge, evapotranspiration, and soil moisture data. Without calibration, the model cannot yet be used for an assessment of ecosystem services. For illustrative purposes, however, Figure 3 shows the model results for water balance, including annual average precipitation, evapotranspiration, and percolation in the WMA.

Changing input data on water use, the SWAT model predicts different outputs (such as river discharge, aquifer recharge, biomass production, and soil erosion). Changing outputs will reveal the impacts on ecosystem services due to changes in water use (including the use of non-conventional water such as desalinated water and treated wastewater). The same approach will be used for climate change and land use change.

Virtual water flows to Israel and impact on global ecosystem services

Due to the limited availability of water and agricultural land, Israel depends on food imports. The water used for crop production in the exporting country is called “virtual water”. Israel is a net importer of virtual water and is almost entirely dependent on international trade when it comes to the staple crops wheat, maize, and soybeans. The import of virtual water is usually accompanied by an “export” of adverse impacts on distant ecosystems, which include deforestation, loss of habitat, soil erosion, and nutrient pollution.

Figure 4: Watersheds used for regional SWAT model coupling

In the MedWater project, we couple multiple regional SWAT models to assess virtual water flows and impacts on ecosystem services. In collaboration with our partners at Ben-Gurion University, representative exporting watersheds were identified in the USA, Brazil, and the Ukraine. We decided to focus on a selection of crops highly relevant for food security in Israel and crops that represent the majority of imports in terms of total weight. Consequently, exporting watersheds were selected that reflect the type of crop production that likely results in imports to Israel, while also taking into account hotspots of ecological impacts (e.g., deforestation hotspots in Brazil). The identified watersheds vary significantly with respect to environmental conditions such as soil types, precipitation, temperature, and impacts on habitats and biodiversity.

Two SWAT models for the USA are currently being finalized, the focus areas are watersheds in Kansas and Iowa. The dominant crops in Kansas are wheat and corn, in Iowa they are soybean and corn. The models are currently being calibrated.