A new study has found that the atmosphere, particularly over arid regions, has not been experiencing the increase in humidity that the Clausius-Clapeyron relationship predicts should accompany the temperature rise it is undergoing. General climate models (GCMs) that incorporate that relationship predict higher relative humidity values than are being seen in arid regions. The difference is sufficient to have significant effects, particularly with regard to increased fire risk and fresh water supply as temperatures continue to rise. Scientists have not identified the cause of this difference but their are several possibilities. Good information is required for resource management and fire prevention programs.
Abstract
Arid and semi-arid regions of the world are particularly vulnerable to greenhouse gas–driven hydroclimate change. Climate models are our primary tool for projecting the future hydroclimate that society in these regions must adapt to, but here, we present a concerning discrepancy between observed and model-based historical hydroclimate trends. Over the arid/semi-arid regions of the world, the predominant signal in all model simulations is an increase in atmospheric water vapor, on average, over the last four decades, in association with the increased water vapor–holding capacity of a warmer atmosphere. In observations, this increase in atmospheric water vapor has not happened, suggesting that the availability of moisture to satisfy the increased atmospheric demand is lower in reality than in models in arid/semi-arid regions. This discrepancy is most clear in locations that are arid/semi-arid year round, but it is also apparent in more humid regions during the most arid months of the year. It indicates a major gap in our understanding and modeling capabilities which could have severe implications for hydroclimate projections, including fire hazard, moving forward.
