Just searching google on environmental news and it seems that soil moisture levels are decreasing, and have been decreasing for some time and it’s becoming quite an issue for farmers. When taught about climate change/global warming, we were told ice melts, sea levels rise, there’s more storms etc. This doesn’t make much sense to me, which is why I’m asking because I want to understand, that if sea levels are rising, and we have MORE water on earth because of melting ice caps, thawing of permafrost etc. that we also have less soil moisture. It seems to me, the opposite would be true, that with all the “New” water we would have more rain and more moisture. As a simpleton, I’d love for you all to explain how it creates lower moisture content so I can share with others HOW and WHY this is the case, also any links to historical maps and data or visuals would be most appreciated!
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This is going to be a pretty shallow answer, but soil moisture (SM) in any place largely reflects a balance between precipitation (P – adds water – increases soil moisture) and evapotranspiration (ET – removes water – decreases soil moisture), i.e., SM ~ P – ET. So, decreasing soil moisture can reflect a decrease in precipitation, an increase in evapotranspiration, or some combination thereof.
From the absolute simplest perspective, increasing average temperatures would tend to increase potential evapotranspiration, so from that perspective (and in the context that in most places climate change implies some amount of increase in average temperatures), even if precipitation was not changing at all, the general expectation would be a decrease in soil moisture (though in reality, ET is not increasing everywhere). In many places, amounts of precipitation are changing, but the assumption that climate change universally implies an increase in precipitation everywhere is flawed. The reasons for this are complicated and vary by area, but if you look at direct measures of these trends globally (e.g., Greve et al., 2014), you’ll see that some areas are getting wetter (i.e., P-ET is getting larger), other places are getting drier (i.e., P-ET is getting smaller), and other places are kind of staying the same (which may reflect limited change in P and ET or changes in P and ET that are counterbalanced such that P-ET is staying nearly the same). In this context, changes in sea level are not terribly relevant and links between sea level and precipitation (on land) are complicated, to put it mildly, where there is not necessarily a direct causative relationship between the two in the way that seems to be assumed.