Reconstructing hydrological drought in Irish catchments (1850–2015)

Climate and Society in Ireland is a collection of essays, commissioned by the Royal Irish Academy, that provides a multi-period, interdisciplinary perspective on one of the most important challenges currently facing humanity. In Chapter 12, Simon Noone and Conor Murphy (both of Maynooth University) attempt to reconstruct monthly river flows for twelve Irish catchments using quality assured long-term precipitation records for the period 1850–2015. 

In recent years significant progress has been made in developing long-term, quality assured records of precipitation for the island of Ireland that stretch back to the eighteenth and nineteenth centuries. These records have been used to extend understanding of past climate variability and change, and to provide further insight into extremes of floods and droughts. For such hydro-climatic extremes it is particularly beneficial to have long river flow records to examine, among other things, how meteorological extremes propagate into hydrological extremes. However, river flow records of concurrent length do not exist on the island. The commencement of river flow monitoring typically coincided with the onset of arterial drainage in the 1940s/1950s and with the occurrence of drought in the mid-1970s when local authorities became concerned about ensuring adequate supply to meet demand.

In the UK and elsewhere, researchers have used long rainfall records to reconstruct river flows for numerous catchments with the derived series being employed to assess variability and change in flow sequences and to investigate past extremes. Reconstructed flows have also been used to assess the resilience of water company drought plans, noting that severe droughts of the nineteenth century are particularly useful for testing current and future water supply systems and to provide a baseline for climate change adaptation planning. For instance, river flow reconstruction and drought analysis for the Anglian Region, United Kingdom (UK) highlighted periods of prolonged drought in 1854–60 and 1893–1907. While similar work for the Severn Trent water supply region in the UK identified several notable drought periods in the reconstructed flow series in 1887–89, 1892–97, 1921–23, 1933–35, 1975–77 and 1995–98. Each of these studies highlights the utility of long-term reconstructed river flows to water planning and to understanding variability and change in catchment hydrology.

This paper aims, firstly, to use the Island of Ireland Precipitation (IIP) network 1850–2015 to reconstruct monthly river flows for selected catchments and, secondly, to identify hydrological droughts in reconstructed flow records. The paper is organised as follows; first we describe the study catchments and detail the data used in reconstructing river flows. Next, we describe the methods, including the hydrological model employed, its calibration and verification. The drought indicators employed are also described. Following the presentation of results we provide some discussion of key insights and future research directions, before drawing conclusions.

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