Climate change isn’t just about temperature. Whilst some may welcome a few more degrees C on the future thermometer and others lose their homes due to sea-level rise, rainfall should probably be higher on the worry list. With an ever increasing population to sustain, drinking water and food production will put added pressure on an already scarce resource (yes, even here in the damp UK water is a finite resource). Well the simplified explanation for changes in rainfall predicted for a warmer climate are that the dry regions get drier and the wet regions get wetter. Well many in the palaeoclimate community will say this simplification is rubbish (myself included) and a new study in Nature Geoscience has assessed historical records and come to the same conclusion. Hydrological changes under warmer climates are not straightforward or simple. If we were to travel back 15 million years to the Middle Miocene Climatic Optimum, an interval of extreme global warmth, we would struggle to spot a Sahara Desert. In fact the arid regions on Earth seem to be linked to moutain uplift (creating rain shadows) and the growth of the polar ice sheets. So what does this mean for the future? Well that is still to come and only through modelling will we gain any sort of prediction.
Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter’ pattern, compared to 9.5% of global land area with the opposite pattern, that is, dry gets wetter, and wet gets drier. We conclude that aridity changes over land, where the potential for direct socio-economic consequences is highest, have not followed a simple intensification of existing patterns.