Abstract

Abstract. Obtaining climate grids describing distinct variables is important for developing better climate studies. These grids are also useful products for other researchers and end users. The atmospheric evaporative demand (AED) may be measured in terms of the reference evapotranspiration (ETo), a key variable for understanding water and energy terrestrial balances and an important variable in climatology, hydrology and agronomy. Despite its importance, the calculation of ETo is not commonly undertaken, mainly because datasets consisting of a high number of climate variables are required and some of the required variables are not commonly available. To address this problem, a strategy based on the spatial interpolation of climate variables prior to the calculation of ETo using FAO-56 Penman–Monteith equation was followed to obtain an ETo database for continental Spain and the Balearic Islands, covering the 1961–2014 period at a spatial resolution of 1.1 km and at a weekly temporal resolution. In this database, values for the radiative and aerodynamic components as well as the estimated uncertainty related to ETo were also provided. This database is available for download in the Network Common Data Form (netCDF) at https://doi.org/10.20350/digitalCSIC/8615 (Tomas-Burguera et al., 2019). A map visualization tool (http://speto.csic.es, last access: 10 December 2019) is available to help users download the data corresponding to one specific point in comma-separated values (csv) format. A relevant number of research areas could take advantage of this database. For example, (i) studies of the Budyko curve, which relates rainfall data to the evapotranspiration and AED at the watershed scale, (ii) calculations of drought indices using AED data, such as the Standardized Precipitation–Evapotranspiration Index (SPEI) or Palmer Drought Severity Index (PDSI), (iii) agroclimatic studies related to irrigation requirements, (iv) validation of climate models' water and energy balance, and (v) studies of the impacts of climate change in terms of the AED.

Highlights

  • Reference evapotranspiration (ETo) is a theoretical variable describing the evapotranspiration that would occur from a well-watered reference surface under specific meteorological conditions (Allen et al, 1998)

  • The original dataset contained data corresponding to the daily maximum temperature (Tmax), minimum temperature (Tmin), wind speed (W ), relative humidity (RH) and sunshine duration (SD) and was provided by Spanish Meteorological Agency (AEMET) across the whole region of Spain

  • The climate series homogeneity was tested after gap filling to (i) detect inhomogeneities introduced by the gap-filling process and (ii) determine if the process was more reliable if the time series had no gaps

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Summary

Introduction

Reference evapotranspiration (ETo) is a theoretical variable describing the evapotranspiration that would occur from a well-watered reference surface under specific meteorological conditions (Allen et al, 1998). A method focused on overcoming the above-mentioned problems related to data availability was designed to generate a climate grid of ETo over continental Spain and the Balearic Islands with a spatial resolution of 1.1 km covering the 1961– 2014 period with a weekly temporal resolution. This method took advantage of two estimation processes prior to ETo calculation: (i) gap filling, used to obtain a subset of the complete time series over the period of interest for each of the climatic variables, and (ii) spatial interpolation, used to generate climate grids of each of the required climate variables.

Data sources
Methodology
Gap filling
Homogenization
Interpolation
ETo calculation
Uncertainty estimation in the climatic grids
Uncertainty propagation
Using 2010–2014 data to validate the air humidity and wind speed grids
Interpolation validation
Spatial and temporal validation using LOO-CV
The 2010–2014 validation
Uncertainty validation
Findings
Discussion and conclusions
Full Text
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