Abstract

In this study, we identified the critical transitions of hydrological processes including precipitation and potential evapotranspiration by analysing their early-warning signals and system-based network structures. The statistical early-warning signals are manifest in increasing trends of autocorrelation and variance in the hydrology system ranging from regional to global scales, prior to climate shifts in the 1970s and 1990s in agreement with observations. We further extended the conventional statistics-based measures of early-warning signals to system-based network analysis in urban areas across the contiguous United States. The topology of urban precipitation network features hub-periphery (clustering) and modular organization, with strong intra-regional connectivity and inter-regional gateways (teleconnection). We found that several network parameters (mean correlation coefficient, density, and clustering coefficient) gradually increased prior to the critical transition in the 1990s, signifying the enhanced synchronization among urban precipitation pattern. These topological parameters not only can serve as novel system-based early-warning signals to critical transitions in hydrological processes, but also shed new lights on structure-dynamic interactions in the complex hydrological system.

Highlights

  • The hydrological cycle plays an important role in the changing Earth’s climate system, especially via the exchanges of heat 20 and moisture between the atmosphere and the Earth’s surface (Chahine, 1992; Held and Soden, 2006; Oki and Kanae, 2006)

  • The occurrence of critical transitions in precipitation patterns was in agreement with recorded observation, consistent with climate shifts in 1970s and 1990s due to low frequency variability such as SST or Interdecadal Pacific Oscillation (IPO)

  • We applied the analysis to the longterm global scale 335 precipitation and potential evapotranspiration (PET) time series as well as city scale precipitation dataset in contiguous United States (CONUS)

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Summary

Introduction

The hydrological cycle plays an important role in the changing Earth’s climate system, especially via the exchanges of heat 20 and moisture between the atmosphere and the Earth’s surface (Chahine, 1992; Held and Soden, 2006; Oki and Kanae, 2006). As compared to temperature shifts, changes in global hydrological cycle (e.g. precipitation) are relatively less wellunderstood, despite the strong coupling between energy and water transport (Allen and Ingram, 2002; Marvel and Bonfils, 2013; Yang et al, 2019). Andrews et al (2010) pointed out that the precipitation response to climate change can be roughly split into a fast response part strongly correlated with radiative forcing absorbed by the atmosphere and a relatively slow 25 response to global surface temperature change.

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