**3. Hamoun lakes**

166 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

beds that become the Hamoun wetlands during wet years.

the Hamoun lakes complex [10].

lakes in Sistan on June 15, 2004.

a halt.

capacity of 1,495,000 acre-feet (1,844 million cubic meters). About 300 miles (482.8 kilometers) of concrete-lined canals were built to distribute the reservoir waters [9]. The Hirmand river is the longest river in Afghanistan (ca. 1150 km; catchment > 160,000 km2) and the main watershed for the Sistan basin, finally draining into the natural swamp of

Severe dust plumes usually extend from Sistan into southern Afghanistan and southwestern Pakistan obscuring the surface over much of the region (Fig 2). Severe droughts during the past decades, especially after 1999, have caused desiccation of the Hamoun lakes leaving a fine layer of sediment that is easily lifted by the wind [55], thus modifying the basin to one of the most active sources of dust in southwest Asia [56, 50, 57]. Therefore, the Hamoun dry-lake beds exhibit large similarities with the other two major dust source regions of the world that comprise of dried lakes and topographic lows, i.e. Bodele depression in Chad [3] and lake Eyre in Australia [4]. The strong winds blow fine sand off the exposed Hamoun lake beds and deposit it to form huge dunes that may cover a hundred or more villages along the former lakeshore. As a consequence, the wildlife around the lake has been negatively impacted and fisheries have been brought to

Fig. 2 (left panel) shows a severe dust storm over the Sistan region as observed from the Terra-MODIS satellite's true color image on 15 June 2004. The intense dust plumes form a giant U-shape extending from Sistan into southern Afghanistan and southwestern Pakistan that obscures the surface over much of the region. The pale color of the dust plume is consistent with that of dried wetland soils. The dust is blowing off the dry lake

**Figure 2.** MODIS image of dust deflation over southern Afghanistan originating from the dry Hamoun

The Hamoun lakes are situated roughly at the termination of the Hirmand river's inland delta. The Hamoun lakes complex (Hamoun-e-Puzak, Hamoun-e-Sabori and Hamoun-e-Hirmand and Baringak) are located in the north of the Sistan region, which is also the largest fresh water ecosystem of the Iranian Plateau and one of the first wetlands in the Ramsar Convention [58]. Water in the Hamoun lakes is rarely more than 3 meters deep, while the size of the lakes varies both seasonally and from year to year. Maximum expansion takes place in late spring, following snowmelt and spring precipitation in the mountains. In years of exceptionally high runoff, the Hamoun lakes overflow their low divides and create one large lake that is approximately 160 kilometers long and 8–25 kilometers wide with nearly 4,500 square kilometres surface area. Overflow from this lake is carried southward into the normally dry Gaud-i Zirreh (Fig. 1), the lowest playa (463-meter altitude) in the Sistan depression. Furthermore, mountain runoff varies considerably from year to year; in fact, the Hamoun lakes have completely dried up at least three times in the 20th century [9]. The maximum extent of the Hamoun lakes following large floods is shown in Fig. 4, where a continuous large lake has been created covering an extended area of ~4,500 km2 with a volume of 13000 million m3 in Sistan and southwestern Afghanistan. This figure corresponds to spring of 1998 after snowmelt in the Afghanistan mountains that transferred large quantities of water into the Hamoun Basin. As a consequence, livelihoods in the Sistan region are strongly interlinked with and dependent on the wetland products and services, as well as on agricultural activities in the Sistan plain. Fishing and hunting represent an important source of income for many households and, therefore, the local and regional economy is strongly dependent on weather conditions, precipitation and land use – land cover changes. The political boundary between Iran and Afghanistan splits the Hamoun system, further complicating management possibilities in the area. Most (90%) of the watershed is located in Afghanistan and practically all of the wetlands' water sources originate there. The Iranian part is desert, and produces runoff only in rare cases of significant local rainfall [10].

In view of the Hirmand and the surrounding rivers that supply most of the sediments to the Hamoun lakes, a brief encapsulation of the relevant geology of the catchment area in Afghanistan is given. Afghanistan has a very complex geology, encompassing two major relatively young orogenies, Triassic and subsequent Himalayan, resulting in amalgamation of crustal blocks and formation of concomitant ophiolites and younger clastic and carbonate sedimentary rocks as well as basaltic lavas and, more recently, extensive alluvial and eolian detritus [59] . The Sistan region and Hamoun dry lake beds are mainly composed of Quaternary lacustrine silt and clay material as well as Holocene fluvial sand, silt and clay (Fig. 3). These materials have been carried to the basin by the rivers, while along their courses Neogene fluvial sand, eolian sand, silt and clay are the main constituents. Note also the difference in the soil-dust composition between two major desert areas, Registan and Dasht-i-Margo in Afghanistan. The former is composed of Neogene coarse gravels and the latter of Quaternary eolian sand. More details about the geology in the Sistan region can be found in [60].

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 169

The Sistan Basin has recently experienced an unusually long 10-year drought starting in 2000 [10]. Combined with war and severe political disruption over the past 2 decades, the 10-year drought has created conditions of widespread famine that affected many people in eastern Iran and southwestern Afghanistan. A suggested, climatic forcing mechanism has been proposed for the recent drought by Barlow and others (2002). A prolonged ENSO (El Niño-Southern oscillation) cold phase (known as La Niña) from 1998 to 2001 and unusually warm ocean waters in the western Pacific appear to have contributed to the prolonged drought. The unusually warm waters (warm pool) resulted in positive precipitation anomalies in the Indian Ocean and negative anomalies over central Afghanistan [64], thus contributing to the drying of the Hamoun Basin. The contrast between a relatively wet year in 1976 and the nearly dry Hamoun lakes in 2001 is shown in Figs. 2 and 4. Millions of fish and untold numbers of wildlife and cattle died. Agricultural fields and approximately 100 villages were abandoned, and many

Most of the Sistan population lives near the Hamoun lakes and is employed in agricultural, fishery, handicrafts and other jobs. To counter the effects of droughts, the Iranian government prepares facilities such as food and flour supplies, medicine and health services and employment in the region to prevent the forced emigration of people, but the continuous and extreme droughts have forced some people to leave the Sistan region. Long droughts at the end of the 1960s, middle of the 1980s, and from 1999 to 2010 affected the Sistan region significantly and resulted in desiccation of the Hamoun lakes, making the surrounding lands saline and disturbing their soil fertility, while some places became barren (see Fig. 5). The most important findings in Fig. 5 are: (1) in 1976, the Hamoun lakes were still thriving. Dense reed beds appear as dark green, while tamarisk thickets fringing the margins of the upper lakes show up as pink shades in the satellite images (Fig. 5). Bright green patches represent irrigated agricultural lands, mainly wheat and barley. The lakes flood to an average depth of half a meter, denoted by lighter shades of blue, while dark blue

**Figure 5.** Satellite (Landsat) images of the Hamoun Basin in spring of different years. Hamoun lakes are fed primarily by water catchments in neighbouring Afghanistan. In 1976, when rivers in Afghanistan were flowing regularly, the lake's water level was relatively high. Between 1999 and 2011, however, drought conditions caused frequent dryness of the Hamoun lakes that almost disappeared in 2001 after

**4. Droughts in the Sistan** 

a 3-year intense drought period [65].

succumbed to blowing sand and moving dunes [65].

**Figure 3.** Geological map of the Sistan Basin and southern Afghanistan *[61-63].*

**Figure 4.** Position of the Hamoun Lakes in Iran and Afghanistan, showing a maximum inundation period.
