Climate change: part 1

 Climate change is a huge topic for any geographer (unless you are a human geographer then the use of social spaces may float your metaphorical boat)! The academic scene is blooming with studies analysing the implications of climate change. Papers focusing on the implications on crop yields and food security are of particular use for this blog. My previous post (in which I referred to Gaun’s paper, which is well worth a read, even if I do say so myself!) gave a brief overview of the influences of future rainfall variations on crop yields. In this post I thought I would take a step back and assess the general implications of climate change for rainfall and temperature. This will help me take critical stance when reading such academic papers.

Temperature

Under mean emissions scenarios, the CMIP 5 projections estimate, by the end of the 21^st century (2070-2099) African surface temperatures will have risen by 2-4 degrees Celsius; values which are robust across the majority of GCM models used in Aloysius et al (2015). Increased levels of evapotranspiration can decrease reliability of surface stores of water and increase the risk of water stress.

Rainfall

Predicating future rainfall patterns is much harder than predicting their partner in crime, temperature.  In simple terms the wet is going to get wetter and the dry is going to get drier (The Guardian, 2011) Now, I am a geography student and that explanation doesn’t quite make the cut.

Increased temperatures allow a greater volume of water vapour to be held in the atmosphere (up to 7% per degree of warming) which could result in an approximate rise of mean annual precipitation by 1-2% (per degree of warming) (Feng et al., 2013). In relation to the global distribution of rainfall, it is predicted that higher latitudes will receive more rainfall at the expense of regions in the tropics (IPCC, 2007). Details surrounding changes in frequency and intensity of rainfall patterns, in Africa, can be found in my previous post. Climate change is predicted to alter, not only the magnitude of rainfall, but also its seasonal distribution and variability. Arid and Semi-arid regions, such as Africa, will be hit the hardest these changes as they rely on seasonal regimes of rainfall for agricultural production.

The typical African diet is reliant on a diet of rain fed crops. This fact indicates these impacts will be particularly felt across Africa, more so than other regions (Desanker, 2002). Changes to both actual evapotranspiration (reducing the water retained in soil and surface stores) and increased variability in rainfall events will reduce the reliability and consistency of crop yields. The Tanzanian report on climate change indicates areas which receive 1 annual rain event (ie. The lower latitudes) will experience a reduction in mean annual precipitation. The report continues by stating this will cause a 33% decline in maize yields (a staple crop in Tanzania). Such a statement suggest changes to future rainfall patterns will dominate crop yields in Africa. This hypothesis lies outside this blog post but I shall return to the topic of temperature vs rainfall for crop yields.

I aim to use this information to help accurately analyse the large body of literature using crop models to simulate agricultural yields under climate change scenarios. Over the next few blog posts I intend to continue reading through the mass of academic literature, examine the consistency of study results and assess the application of such studies in aiding policy decisions.