Comparing Long-term Runoff and Precipitation Trends Worldwide

Life on Earth depends on how water availability will be affected by anthropogenic climate change. One pressing question is how changes in terrestrial water-dependent variables, like runoff, soil moisture, and vegetation, will differ from precipitation trends. Will climate change result in the reduction or enhancement of water availability? Therefore, our broader research goal is to compare local precipitation trends with local trends of other water-dependent variables in as many places as feasible. This study begins this broader research effort by analyzing long-term, historical runoff trends and comparing them to co-located precipitation trends. This study will use observational runoff data from the Global Streamflow Indices and Metadata Archive (GSIM), which is comprised of unimpaired and/or naturalized runoff time series from gauged river basins around the globe. Once these trends are computed over several time intervals, they will be compared to long-term precipitation trends calculated using data from the Climatic Research Unit Time Series (CRU TS) and the Global Precipitation Climatology Centre (GPCC) databases. From these results, we will determine the extent to which long-term standardized runoff trends are more negative or positive than precipitation trends. This will give us insight into whether runoff trends are directed more by precipitation or by another variable. More negative runoff trends than precipitation trends would suggest rising global temperatures and/or vegetation greening have more influence on runoff, while more positive runoff trends than precipitation trends would imply that runoff is more strongly dictated by the increasing intensity of rainfall events and/or leaf stomatal closure. These results will contribute to our broader research efforts in the future by comparing them to local trends of other water-dependent variables, such as vegetation.