How the climate regime of the MENA region influences its water resources


The Middle East and North Africa (MENA) region faces unique challenges in environmental sustainability and human habitation. The first and most important of these is the limited availability of fresh water. As a wide swath of arid to dry subhumid mountainous desert, the region sees most of its precipitation fall as mountain snow. Surface water is relatively scarce, and major streams are fed by snowmelt runoff from source areas far from major points of use. The headwaters of the Tigris and Euphrates rivers in the mountainous east of Turkey and the headwaters of the Blue Nile in the Ethiopian highlands are prime examples. The sustainable availability of water for these river systems therefore depends on the predictable transformation of mountain snow cover into runoff.

The relative hydrological “health” of a system is often considered in terms of the absolute amount of precipitation falling on the watershed. If the amount of precipitation is significant, precipitation alone does not guarantee runoff. A basin’s ability to effectively convert precipitation into runoff depends on a complex and sensitive interplay of forces that must align to be predictable – and predictability is the foundation of sound planning.

Hourly

Water stores energy more efficiently than air. The oceans are therefore an important reservoir of heat produced by human activity. Unsurprisingly, temperature anomalies in the ocean have become significantly skewed upper since the 1990s. This is important because warming oceans have the potential to bring more moisture to the atmosphere through increased evaporation. A warming of the air masshowever, mitigates this effect with an increased ability to retain moisture, which means that more moisture is needed to reach saturation. This impacts both the amount and timing of precipitation. In other words, when coupled with a warming ocean, a warmer atmosphere may take longer to reach saturation, but will produce more precipitation when it does.

Studies suggest that humid regions will become wetter and arid regions will have even less precipitation. For regions already feeling the effects of rising average temperatures and aridification – such as the MENA region – longer, hotter summers and the late onset of cooling and autumnal precipitation can mean both a delay in the formation of the snowpack and a decrease in the snowpack. This may be the result not only of insufficient humidity in the atmosphere needed to reach saturation, but may also be due to more winter precipitation falling as rain rather than snow. The potential coupling of warmer oceans and a warmer atmosphere has important and possibly disastrous implications for the predicted lifetime of surface waters in the MENA region.

Pre-existing conditions

Some regions have naturally more favorable conditions than others for generating runoff. Areas with cooler, wetter fall weather at higher elevations have soils at (or close to) saturation before the snow accumulation season. This is important because the state of the “soil moisture balance” is often an influencing factor in the amount of runoff generated during melting. In this context, a soil closer to saturation will have a reduced ability to retain additional water. Thus, snow that accumulates on saturated ground will be more likely to generate runoff with the onset of spring melt.

In contrast, a warmer atmosphere with longer, hotter summers will have a drier prelude to the snowpack season. The warmer air draws moisture away from the soil surface and increases evaporative stress on regional vegetation, resulting in a soil moisture “deficit” during this crucial time. Since a greater percentage of meltwater must first be absorbed into the soil, less runoff will be generated.

dust on the snow

The sun also plays an important role in this process. The development of the snowpack is sensitive to the daily fluctuation in/out of solar radiation in the atmosphere. Snow reflects most incoming solar radiation. Snow that has accumulated on saturated ground after a wet fall reflects more effectively. However, snow that has accumulated after a long, hot summer and dry autumn may continue to accumulate dust on the surface of the snowpack, which absorbs solar radiation, increases the temperature at the surface of the snowpack, and tends to cause a premature melting.

Cumulative effect

Governments in the MENA region have invested money in the development of large-scale hydroelectric and water projects. Perhaps the most notable of these is that of Turkey Southeast Anatolia Project (GAP), a series of 22 dams, 19 hydroelectric facilities and agricultural diversions in the upper reaches of the Tigris and Euphrates, and most recently the Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile in Ethiopia. Both megaprojects were designed to stimulate economic growth and ensure greater independence. The benefits of these projects, however, may be overestimated if the quantity and quality of runoff prove increasingly disappointing.

Seasonal precipitation totals are significant, but even the wettest years will have reduced runoff if delivery timing is off, fall has been warm and dry, and an already meager snowpack is melting earlier than expected. In these years, a greater soil moisture deficit must be overcome before the watershed can generate spring runoff.

Reduced flow can also have adverse effects on water quality. Reduced runoff means less freshwater available to dilute eroded natural salts from upstream areas, resulting in higher salinity in surface waters and agricultural soils. Hotter, drier conditions for a greater percentage of the year mean less irrigation water available to flush out salts that build up in the soil. Increasing soil and surface water salinity poses an existential threat to agriculture as well as an economic liability (in terms of damage to pipes, sewers and other infrastructure).

These impacts can be mitigated through careful planning that considers this delicate balance of factors, such as coordinated facility management to minimize negative impacts on all users or funding arrangements designed to address damage caused by excessive salinity. . Greater cross-border collaboration between countries in the MENA region is essential if stakeholders hope to maximize the delivery potential of the water resources projects in which they have already invested so much.

Orestes Morfín is a senior planning analyst at the Central Arizona Water Conservation District and a nonresident researcher with MEI’s Climate and Water program. The opinions expressed in this article are his own.

Photo by Burak Kara/Getty Images

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