Observed variability and trends in global precipitation during 1979–2020

Abstract

How global precipitation might have changed on the interdecadal-to-multi-decadal time scales during the satellite (post-1979) era is examined by means of the satellite-based GPCP V2.3 monthly precipitation analysis. Comparisons with the results from CMIP6 and AMIP6 are further made in terms of global mean precipitation change and regional features of precipitation change, aiming to provide not only an improved understanding of the effects of major physical mechanisms on precipitation change, but also an assessment of the skills of current climate models and likely some clues for diagnosing possible limitations in observed precipitation. Long-term change/trend in global mean precipitation is generally weak in GPCP. Although the GPCP trend is statistically significant at the 90% confidence level over global land + ocean during 1979–2020, it is not significant over either global land or ocean separately. For the shorter, overlap period with the CMIP6 historical experiments (1979–2014), GPCP positive trends can’t reach the 90% confidence level, while significant and more intense precipitation trends appear in CMIP6 ensemble-means. However, a roughly similar global sensitivity to surface temperature change can be derived in GPCP, CMIP6, and AMIP6, providing confidence in both observed and simulated global mean precipitation change. Large regional trends with positive and negative values can readily be seen across the world in GPCP. AMIP6 can generally reproduce these large-scale spatial features. Comparisons with CMIP6 confirm the combined effects from anthropogenic greenhouse-gases (GHG) forcing and internal modes of climate variability such as the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). Limiting the PDO/AMO effect makes the trend patterns in GPCP residuals more similar to those in CMIP6, implying that the GHG effect would become more readily detectable in observed precipitation in the near future with regards to both global mean and regional precipitation changes. Furthermore, similar changes in precipitation seasonal range, especially over global lands, occur in GPCP, CMIP6, and AMIP6, suggesting that the GHG effect might already be discernible in certain aspects of precipitation change.