Observational evidence for cloud cover enhancement over western European forests

Abstract

Forests impact regional hydrology and climate directly by regulating water and heat fluxes. Indirect effects through cloud formation and precipitation can be important in facilitating continental-scale moisture recycling but are poorly understood at regional scales. In particular, the impact of temperate forest on clouds is largely unknown. Here we provide observational evidence for a strong increase in cloud cover over large forest regions in western Europe based on analysis of 10 years of 15 min resolution data from geostationary satellites. In addition, we show that widespread windthrow by cyclone Klaus in the Landes forest led to a significant decrease in local cloud cover in subsequent years. Strong cloud development along the downwind edges of larger forest areas are consistent with a forest-breeze mesoscale circulation. Our results highlight the need to include impacts on cloud formation when evaluating the water and climate services of temperate forests, in particular around densely populated areas.

Simulating damage for wind storms in the land surface model ORCHIDEE-CAN (revision 4262)

“…(Randerson et al, 2006), the direct and indirect effects of wind disturbances may contribute to the top of the atmosphere radiative forcing (O'Halloran et al, 2012). The direct effects, such as a reduction in leaf area index (Juárez et al,5 2008), transpiration (Negrón-Juárez et al, 2010), an increase in the surface albedo (Planque et al, 2017), and roughness (Zhu, 2008) have been shown to impact the regional climate, i.e., following the storm Klaus in 2009, cloud cover frequency was observed to decrease over Les Landes in Southwestern France (Teuling et al, 2017). The indirect effects include a reduction of the gross productivity by damage to the rooting system, increased tree mortality due to facilitating insect or pathogen outbreaks (Sturrock et al, 2011), or a change of the forest ecosystem by shifting canopy structure to an old-growth with short stature 10 (Lin et al, 2017).…”

“…Furthermore, storm-induced disturbances are likely to provide feedbacks on climate through direct effects such as increasing greenhouse gas emissions (Lindroth et al, 2009), increasing surface albedo (Planque et al, 2017), and decreasing local cloud 10 frequency (Teuling et al, 2017) as well as indirect effects such as increased natural disturbances, a reduced logging rate in subsequent years, increased weathering, and increased C, N and cation leaching (Futter et al, 2011;Köhler et al, 2011).…”

A global assessment of gross and net land change dynamics for current conditions and future scenarios

“…These differ for each land system per world region. A land system map for the baseline year 2000, which is based on census and remote sensing data (van Asselen and Verburg, 2012), can be seen in Fig. 3.…”

“…This model uses a land system classification instead of the more traditional land cover classification (van Asselen and Verburg, 2012). Land systems are described by a set of fractional land cover classes consisting of built-up, cropland, grassland, forest, and other land co-occurring in spatial simulation units of 9.25 × 9.25 km pixel.…”

“…To assess gross and net land changes for a future scenario, we used simulation output from the land system model CLUMondo (van Asselen andVerburg, 2012, 2013). This model uses a land system classification instead of the more traditional land cover classification (van Asselen and Verburg, 2012).…”