Soil moisture and vegetation controls on evapotranspiration in a heterogeneous Mediterranean ecosystem on Sardinia, Italy

Abstract

[1] Micrometeorological measurements of evapotranspiration (ET) can be difficult to interpret and use for validating model calculations in the presence of land cover heterogeneity. Land surface fluxes, soil moisture (q), and surface temperatures (T s ) data were collected by an eddy correlation-based tower located at the Orroli (Sardinia) experimental field (covered by woody vegetation, grass, and bare soil) from April 2003 to July 2004. Two Quickbird high-resolution images (summer 2003 and spring 2004) were acquired for depicting the contrasting land cover components. A procedure is presented for estimating ET in heterogeneous ecosystems as the residual term of the energy balance using T s observations, a two-dimensional footprint model, and the Quickbird images. Two variations on the procedure are successfully implemented: a proposed two-source random model (2SR), which treats the heat sources of each land cover component separately but computes the bulk heat transfer coefficient as spatially homogeneous, and a common two-source tile model. For 2SR, new relationships between the interfacial transfer coefficient and the roughness Reynolds number are estimated for the two bare soil-woody vegetation and grass-woody vegetation composite surfaces. The ET versus q relationships for each land cover component were also estimated, showing that that the woody vegetation has a strong tolerance to long droughts, transpiring at rates close to potential for even the driest conditions. Instead, the grass is much less tolerant to q deficits, and the switch from grass to bare soil following the rainy season had a significant impact on ET.

Species‐specific transpiration responses to intermediate disturbance in a northern hardwood forest

“…Due to the limited area of the treatment plot (39 ha), the footprint of the flux measurements occasionally included fluxes that originated outside of the disturbed plot. A 2-D footprint model [Detto et al, 2006;Morin et al, 2014] was used to approximate how much of the measured flux came from the disturbed plot on the basis of wind speed, direction, surface roughness height, and atmospheric boundary layer stability. Fluxes for the treatment plot were corrected assuming that the observed total flux for each half hour was a mixture of fluxes from a control-like forest (surrounding the treatment plot) and from the treatment plot itself.…”

Temporal dynamics of soil water balance components in a karst range in southeastern Spain: estimation of potential recharge

“…In Mediterranean regions, due to the scarcity of water resources, reliable evaluation of water lost through evapotranspiration is very important (Rana & Katerji, 2000). Despite the attention that these ecosystems are receiving (Detto et al, 2006), knowledge of E rates in Mediterranean mountain areas continues to be poor. This is due to the difficulty of evaluating E accurately because all the weather variables range over very large intervals and any variation in one parameter immediately influences all the other variables that are mutually linked (Rana & Katerji, 2000), and also due to land cover heterogeneity.…”

Controls on surface soil drying rates observed by SMAP and simulated by the Noah land surface model

“…In situ observations have allowed for investigation of how different environmental factors control soil drying rates and thus evaporation rates (Cavanaugh et al, 2011;Detto et al, 2006;e.g., Kurc andSmall, 2004, 2007). Only recently has satellite remote sensing of soil moisture advanced sufficiently to make it possible to monitor drying rates at large scales (Entekhabi et al, 2010;Kerr, 2006), thus allowing scientists to evaluate the physical controls on soil drying across a wider range of 15 conditions.…”