Projected future water availability in Chad: A national scale - Part two.

Arid northern region of Chad - Source: United Nations Development Programme

So last weeks post looked at the projections for water availability across the whole of Africa. It was based on the findings in the IPCC's forth assessment report. So now we've seen that that continent scale projections, let's look at a national scale case study, Chad. The projections come from the highly informative publication by the USGS, focused on the effects to Chad from climate change (USGS, 2012) and the United Nations Development Programme focused on climate change in Chad (UNDP, 2018). Chad is precariously placed between multiple environmental and climatic zones. The northern region is comprised on a desert zone (The Saharan desert), the central area comprised of a a semi-arid zone (the sahelian belt), with the southern zone a more fertile Sudanian Savana. Due to this, environmental change is going to create and foster non-homogenous externalities for water availability. So now that we've set the context, let's jump into the future water projections. 

Figure 1.1 - Map of Chad

Historic changes: 1950-2009

Climate change has been affecting precipitation and temperatures in Chad for nearly a century. Anthropocentric led climate change has directly affected water availability and security. "Between 2000 and 2009, the average rainfall in Chad’s crop growing regions was about 13 percent lower than the1920–1969 mean average, which is more than 1.3 standard deviations below this mean" (USGS, 2012). Couple this with temperature increases of "more than 0.8° Celsius (°C) across much of Chad since 1975, with typical rates of warming greater than 0.2°C per decade" (USGS, 2012). Whilst this had led to increasing water insecurity across the whole of Chad in general, the northern and central regions have seen the most incrementally significant negative effects due to the decreased precipitation having a more proportional effect on overall precipitation due to the values already being extremely low in this arid environment. Thus, from the data presented in the USGS publication, we can see that from 1950-2009 climate change has already significantly reduced water availability and security in Chad. Therefore, from this, we can without any further data assume that climate change is only going to exacerbate these insecurities in Chad; thus, let's now look at the data for the projections from present into the future!

Future water availability projections:

Future variability of the hydrological regime and fresh water regime is projected to record drastic decreases in fresh water availability in the Lake Chad Basin (LCB). This is due to projected, rising temperatures, changes in the spatial and temporal variability of precipitation and land use/population pressures. However, an interesting finding in the projections is seen in precipitation rates. As we'll see later in this post, there is only a marginal decrease in mean average precipitation rates across Chad; but more of that later! So let's first look at the projections of temperature and its affects on water availability.

Figure 1.2 - Projected change in monthly temperature for Chad for 2080-2099

Figure 1.2 shows the projections for monthly temperature increases between 2080 and 2099. It highlights that there will be increases across all months, however, non-homogenous increases, with September for example seeing increases of up to 5 degrees celsius (bcc csm1 1 projection model). Increases in temperatures such as these projections will dramatically affect water security across the whole of Chad. Evapotranspiration will significantly increase due to the airs increased ability to hold moisture had higher temperatures (Synder, 2011). This will lead to even fairly wet areas of Chad, such as the southern Sudanian Savana, seeing decreased annual precipitation rates. The intertropical convergence zone (ITCZ) will also be directly affected, with its divergence from the equator increasing due to climate change. The wet season in Chad, May to October, coincides with the highest projected monthly temperature increases, thus precipitation that falls in those months is going to be subject to the most significant evapotranspiration forces. This is projected to result in surface water stores being especially vulnerable at the time when they should be filling up and storing water for the dry season. Increases in temperature also directly impact the ITCZ. There is projected to be greater annual variability of the divergence from the equator of the ICTZ, thus, Chad will be directly affected by changes in annual precipitation. This leads succinctly to the next section; the projections for precipitation. 

The most important observation to make is that changes in precipitation are incredibly spatially and temporally variable across Chad. Figure 1.3 and 1.4 below highlight the difference in projections between the northern and southern region of Chad. However, "projections of mean annual rainfall averaged over the country from different models in the ensemble project a wide range of changes in precipitation for Chad.  Projected change range from ‐15 to +9mm per month (‐28 to +29%) by the 2090s, with ensemble means close to zero" (Sweeney et al.). However, a surprising projection for Chad is that mean average precipitation will not see that significant changes. For example, as seen in figure 1.3 (the northern region of Chad), mean average monthly precipitation projects only slight decreases in five months, with another 5 months of projected increases. 

Figure 1.4 on the other hand (the southern region of Chad), highlights that projections show more significant increases in precipitation in specific months than decreases in precipitation. Therefore, it illuminates that Chad is projected to experience only minor changes in precipitation from 2020 to 2099.

Figure 1.4 - projected change in monthly precipitation for 2020-2099 in Southern region of Chad

Overall, this illustrates the key message I want everyone to take every from this post, that climate change in not a linear or homogenous process, with substantial temporal and spatial variability.  Whilst temperatures are projected to increase significantly, precipitation is only projected to change subtly. Hence, it is the forcing factor of increasing temperatures that is going to be the predominant factor affecting water availability due to increased evapotranspiration.

Our next blog is going to look at the socio-political externalities due to water insecurity in Africa.