Impact of climate variability on the hydrology of the Sudd wetland: signals derived from long term (1900–2000) water balance computations
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The Sudd wetland is a huge swampy area (30,000–40,000 km2), with vegetation composed mainly of papyrus, water hyacinth and grasslands. It is located in South Sudan, and is of vital importance for livelihoods, ecosystem services and water resources. Half of the White Nile flow evaporates when passing through the Sudd (~16,000 106 m3/year). Historically, this phenomenon triggered several water conservation projects in the Nile region (the Jonglei Canal Project). However, the available information on the hydrology of the Sudd is very limited, and mostly outdated. This paper investigates the long term dynamics of the Sudd hydroclimatology (water balance components), and how it affects the wetland areal extent. The water balance results show that the extent of the Sudd wetland area is determined both by the regional climate (outflow from Lake Victoria) and the local climate, represented by precipitation and evaporation over the wetland itself. The long term trends of the Sudd hydrology from 1900 to 2000 have been analyzed with the Mann–Kendall test statistics. The water flows into and out of the Sudd demonstrate a statistically significant increasing trends during the last 100 years. This can be attributed to increasing rainfall over Lake Victoria in the early 1960s. The daily maximum and minimum temperature in the Sudd shows an increasing trend of 0.6 and 1.5 °C, respectively, over the last 100 years. However, this has not caused any change of the wetland actual evaporation (open water evaporation plus plant transpiration). The impact of the temperature rise has likely been compensated by a reduction of the relative humidity and solar radiation over the wetland. The statistical test shows that both relative humidity and solar radiation (sunshine hours) has significantly decreased, each reduced by 10 % over the last 50 year. The precipitation over the Sudd showed no significant change during the last 100 years. On the other hand, the areal extent of the Sudd wetland increased by 19,000 km2 (80 %) during the last 100 years, as a result of the increased inflows. The long term variability of the Sudd areal extent provides new results and deeper insights of the two-way land surface climate feedbacks, and informs wetland conservation and water resources management for this important tropical wetland.
KeywordsWetlands Papyrus Hydroclimatology Mann–Kendall Statistical test
The research described here was partly funded by the Netherlands Ministry of Development Cooperation (DGIS) through the UNESCO-IHE Partnership Research Fund (UPaRF).
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