Reforestation efforts and impact on climate change

The Mediterranean basin is strongly affected by global warming leading to important changes in the hydrological cycle and ecosystems. Mean precipitation decrease in the western Mediterranean reduces water availability in the region yielding, together with air temperature increase, loss of forests and desertification. Besides, extreme conditions linked to climate change play an important role in the occurrence of fires enhancing the loss of forest areas. Forests provide an important amount of water vapor to the atmosphere, can help decrease air temperature, and they are crucial in carbon dioxide fixation. In these terms, Mediterranean countries such as Spain, strongly affected by climate change, started reforestation efforts at local-to-regional scales to adapt and mitigate its effects. However, it is key to investigate to what extent these land-use changes influence main hydrometeorological variables and atmospheric dynamics.

In this study, the Weather Research and Forecasting (WRF) model is used to conduct sensitivity analyses regarding the impact of increasing forest mass on the hydrological cycle and atmospheric conditions over the Iberian Peninsula and particularly the Mediterranean coast. To this end, land-use categories have been modified over a control simulation to describe different scenarios. These scenarios are selected regarding the extension of reforested areas, as well as the type of vegetation planted, which are defined with respect to climatological parameters such as mean annual precipitation. The scenarios considered are as follows (i) reforestation with pine forest of bare soils, grasslands and shrublands (PINE1), (ii) same as PINE1 but also reforesting mixed cropland/natural areas (PINE2), (iii) same as PINE2 but with heterogeneous forest (MIXED) and (iv) same as MIXED but with 50% decrease in tree density (MIXED50%). Simulations are conducted at horizontal resolutions of 9 and 3 km for the period 2015-2020 covering the Iberian Peninsula and the Hydrographic Confederations of the Júcar and Segura (CHJS) located in the south-eastern part of the Iberian Peninsula, respectively. The study focuses on the analysis of the spatio-temporal patterns of the main hydrometeorological variables (e.g., precipitation, soil moisture, evapotranspiration and atmospheric water vapor), and the examination of the variability on the chain of processes leading to precipitation.

Preliminary results indicate a generalized increase in annual mean precipitation over the Iberian Peninsula (up to 1% for MIXED), more marked along the Mediterranean coast, together with changes in the distribution of atmospheric water vapor. Main precipitation variations occur during summer, with areas receiving up to three times more precipitation than in the control runs during autumn, some areas near the Mediterranean coast present an increase in seasonal precipitation up to 70% with respect to the control run.