Understanding importance of convective rain events and tracing their impact on catchment with isotopes

The IAEA is calling on research organizations to join a new Coordinated Research Project (CRP) it is launching to improve the understanding of the impact of convective rain events on surface water and groundwater resources using isotopes.

Scientists predict that climate change will modify rainfall patterns in different regions across the world. These modifications in rainfall patterns include prolonged drought phases interrupted by heavy rainfall events, where a significant portion of the yearly rainfall can occur within a couple of hours. This type of rainfall is usually associated with convective rainfall events which are predicted to become more common with rising temperatures. Such events can cause excess overland flow, soil erosion, and urban flooding, especially when occurring over dry and/or sealed land. Flooding and soil erosion impair water quality of drinking water reservoirs. Furthermore, convective rain events probably contribute less to the recharge of aquifers, however, it is not yet clear if this applies to all climate regions and topographical settings. Therefore, integrated water resource management (IWRM) requires a better understanding of the impact of such events on surface and groundwaters.

Water isotopes have proven to be ideal tracers of water movement from the rain drop to the spring, well, river or reservoir. However, convective rain events might challenge our data collection and interpretation techniques since they occur within few kilometres and often comprise the annual isotopic variation of the site in one event. This condensed variation requires high temporal resolution and the development of standardized equipment for automatic sampling.

Isotope-based separation of catchment compartments contributing to discharge assumes that the stream water composition reflects the proportions of different water sources with distinct ranges in isotope values. Hence, to fully understand the impact and legacy of convective rain events, the precipitation data collection needs to be adapted and additional tracers need to be explored to follow the “extreme rain signal” through the catchment. Short-lived radionuclides can unravel timescales of contribution of groundwater, surface runoff and soil water to discharge, providing critical information on vulnerability of the different compartments. Furthermore, water chemistry parameters measured at high frequency at the catchment outlet can be used as an independent evaluation of model predictions of water source and flow path determined with isotopes.

The four year-long new CRP puts forward an innovative approach of high frequency sampling of rain events, sampling of the saturated and unsaturated zone, a suite of isotopes (including stable and radiogenic water isotopes, sulphur-35 and radon-222), in combination with high frequency sensors at the outlet of the catchment. The CRP will revisit the application of isotopes in catchment hydrology on short time scales provoked by convective rain events and provide recommendations for (1) high frequency and event-based sampling of water isotopes, (2) application of short lived radioisotopes, and (3) the combination of isotopes with concentration-discharge relationships obtained by high frequency water quality sensors.

CRP Overall Objective

The overall goal of the CRP is to improve the understanding of the impact of convective rain events on both surface and groundwater resources using isotopes. In this sense, the CRP will particularly contribute to Sustainable Development Goal (SDG) target 6.4 on ensuring freshwater supplies by understanding and predicting the impact of climate change on freshwater resources, as well as feed into the goals of zero hunger (SDG 2.4), climate change resilience, adaptation, impact reduction and early warning (SDG 13.1 and 13.3), and the protection of freshwater ecosystems (SDG 15.1).

Specific Research Objectives

  • Advance the methodology of high frequency sampling for isotopes in precipitation to evaluate the isotopic signal over time of intense rain events.
  • Track the isotopic signal of intense rain events through the catchment and estimate the residence time in the catchment using stable radioisotopes.
  • Combine isotopes, water chemistry and concentration-discharge relationships in rivers to understand the timing of the drainage of different hydrological compartments following convective rainfall and climate change impact.

How to join this CRP

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