7. Developing a Historical Precipitation Record

Knowing historical precipitation is important for climate monitoring and for evaluating coupled climate models designed to simulate changes in precipitation associated with climate change. Over land gauge-based analyses are sufficient to determine large-scale variations over the twentieth century. Over oceans satellite-based analyses can be used beginning 1979. However, there are few direct or remote sensing observations of oceanic precipitation variations before 1979. For the pre-satellite time, it is possible to use reconstructions based on the available data to analyze some oceanic precipitation variations. Evaluations of the available data and methods have shown that large-scale variations in twentieth-century oceanic precipitation may be reconstructed. Reconstructions based on spatial covariance and historical gauge data represent seasonal to interannual variations. Reconstructions based on correlations with sea-surface temperature (SST) and sea-level pressure (SLP) represent multi-decadal variations. Combining these two types of reconstructions yields a merged reconstruction with the best features of both.

This review describes how the reconstructions are developed and discusses their major features. The merged reconstruction indicates increasing precipitation with increasing global temperature, consistent with theoretical estimates. However, the reconstruction indicates that the change is not steady and has a shift associated with the climate shift noted in Pacific SSTs in the 1970s.