Extensive deforestation in catchments in Malawi has led to land degradation leading to ectrensive erosion and gullies. Deforestation has also resulted in changes in soil structure affecting the way water moves on the surface and underground. In this article, the author will show that ecause of deforestation, our lands are degraded and out tivers are raging with floods in the wet season, leading to water shortages for both irrigation and domestic water supplies. Further, it will be shown that extensive soil erosion, as a result of deforestation, has led to too much sedimentation and floating vegetation in rivers. This has led to challenges in power generation in the Shire River leading to blackouts and load shedding.
Deforestation and its impact on the hydrology of rivers and lakes
Extensive deforestation results in loss of vegetative and soil cover which extend to land degradation and changes in the soil structure and properties. Because of high deforestation rates, less rainwater is infiltrating into the ground to replenish groundwater avaiable to streams during the dry season. More surface runoff means rivers and streams bursting their banks resulting in flooding and more sediment loads in the wet season. According to the Department of Desaster Management Affairs (Dodma) the frequency and district distribution of Malawi floods have increased since the year 2000 with more and more districts reporting flooding cases. For example, in 2015, 19 out of 28 districts reported flooding compared to only four before the year 2000. The net effect of low infiltration rates is that even very small storms (less than 30mm) result in a lot of surface runoff and sediment transport to the rivers, cousing extensive flooding and siltation problems. Even more worrying is the fact that Malawi is losing a lot of water during a very short period (December to April) to Zambezi River into the Indian Ocean. The irony is that this excess water being lost to the Zambezu is needed during the dry eight months by many Malawi cities, towns and industries including Electricity Supply Corporation of Malawi, water boards, Illovo Sugar Company, beer companies and irrigation schemes, Unfortunately, there is simply no cheaper way of retaining this water for use during the eight dry months when water is needed. More dams could be constructed upstream at great cost but without checking deforestation upstream, they are likely to be filled up with silt in no time. Furthermore, the consequence of less water entering the ground to become groundwater is that streams and rivers dry up during the dry season or have very low flows. The dry season is the time when demand for water is highest for domestic use and irrigation. According to studies conducted at Luanar’s Bunda Campus, most rivers, including the Shire, are drying up during the dry season or have low base flows. Low base flows in rivers flowing into Lake Malawi or the Shire River in the dry season means low lake levels and low flows in the Shire during the dry season. Lake Chilwa has suffered the same fate with more frequent periodic drying-up un the last ten years. Plans to tap water for Lilongew City out of Lake Malawi need to consider the changing Hydeology of rivers and the lake. Currently, there are already many water withdrawals from Lake Malawi for irrigation and domestic water supply in Malawi, Mozambique and Tanzania. If we rush or do not do up our hydrological homework thoroughly, we may end up with very low levely in Lake Malawi and little or no flows in Shire River. No flows in the Shire River means water shortages for Blantyre City and no irrigation in Nchalo, Chikwawa and Nsanje. Low or no flows in the Shire in the dry season means low or no power production at Nkula, Tedzani and Kapichira hydroelectric power (Hep) plants. Less per generated means more power blackouts and extensive load shedding in the dry season. To partly address this, a new barrage is being constructed at Liwonde to store water in the lake during periods of excess (the wet season) and release it during periods of low flows, ensuring that the Hep plants on the Shire River and Blantyre City have enough water during the dry season. However, without addressing deforestation upstream, changes in the hydrology of rivers will still be there and are likely to get worse with climate change. The new barrage plus afforestation in upstream catchment is the way to go to ensure sustainable water supplies out of the lake into Shire River.
Read more about Deforestation and its impacts on water supplies and Deforestation and its impact on power generation in the article below.