Over the last century extraordinary efforts have been devoted to determining soil erosion rates (in units of mass per area and time) under a large range of climatic conditions and land uses, and involving various measurement methods. We undertook a meta-analysis of published data from more than 4000 sites worldwide. The results show that there is extraordinarily high variability in erosion rates, with almost any rate apparently possible irrespective of slope, climate, scale, land use/land cover and other environmental characteristics. However, detailed analysis revealed a number of general features including positive relationships of erosion rate with slope and annual precipitation, and a significant effect of land use, with agricultural lands yielding the highest erosion rates, and forest and shrublands yielding the lowest. Despite these general trends, there is much variability that is not explained by this combination of factors, but is related, at least partially, to the experimental conditions. Our analysis revealed a negative relationship between erosion rate and the size of the study area involved; significant differences associated with differing measurement methods, with direct sediment measurement yielding the lowest erosion rates, and bathymetric, radioisotope and modeling methods yielding the highest rates; and a very important effect of the duration of the experiment. Our results highlight that, when interpreting erosion rates, the experimental conditions involved must be taken into account. Even so, the data suggest that only order of magnitude approximations of erosion rates are possible, and these retain a very large degree of uncertainty. Consequently, for practical purposes such as calculation of global sediment budgets, empirical equations are not a substitute for direct measurements. Our results also show that a large proportion of the experiments have been short-term (less than 3 years), which reduces dramatically the reliability of the estimated erosion rates, given the highly non-normal behavior of soil erosion (time-dependency). Despite the efforts already made, more long-term measurement experiments need to be performed, especially in regions of the world that are under-represented in global datasets. In addition, protocols need to be established for standardizing the measurement methods and reporting the results, to enable data to be compared among diverse sites.

Abstract. In this study we analyzed the spatial distribution, temporal variability and trends in 13 reference evapotranspiration (ET 0 ) in Spain from 1961 to 2011. Twelve methods were analyzed to 14 quantify ET 0 from quality controlled and homogeneous series of various meteorological variables 15 measured at 46 meteorological stations. Some of the models used are temperature based (e.g., 16Thornthwaite, Hargreaves, Linacre), whereas others are more complex and require more 17 meteorological variables for calculation (e.g., Priestley-Taylor, Papadakis, FAO-Blaney-Criddle). 18The Penman-Monteith equation was used as a reference to quantify ET 0 , and for comparison 19 amongst the other methods applied in the study. No major differences in the spatial distribution of 20 the average ET 0 was evident among the various methods. At annual and seasonal scales some of the 21 ET 0 methods requiring only temperature data for calculation provided better results than more 22

Abstract. An analysis was made of the Precipitation Concentration Index using the new MOPREDAS database of monthly precipitation in Spain (Monthly Precipitation Data base of Spain). The database was compiled after exhaustive quality control of the complete digitalized Spanish Meterological Agency (AEMet) archives and contains a total set of 2670 complete and homogeneous monthly precipitation series from 1946 to 2005. Thus, MOPREDAS currently holds the densest information available for the 1946-2005 period for Spain and ensures a high resolution of results. The Precipitation Concentration Index (PCI) is a powerful indicator of the temporal distribution of precipitation, traditionally applied at annual scales; as the value increases, the more concentrated the precipitation. Furthermore PCI is a part of the well-known Fournier index, with a long tradition on natural system analyses, as for example soil erosion. In this paper, the mean values of annual, seasonal and wet and dry periods of PCI in the conterminous Spain and for two normal periods (1946-1975 and 1976-2005) were studied.Precipitation in Spain follows a general NW-SE spatial pattern during the wet (months) period due to the Atlantic storm track, while during the dry (months) period, it follows a predominantly N-S spatial pattern. As a result, the annual values of PCI combine the two patterns and show a SW-NE PCI gradient.The analyses of the two sub-periods show significant changes in the precipitation occurred in conterminous Spain from 1946 to 2005, and precipitation concentration increased across most of the IP. At an annual scale, PCI increases mostly due to an increase in precipitation concentration during the wet season. At a seasonal scale significant changes were detected between 1945 -1975 and 1976, while changes in Correspondence to: J. C. González-Hidalgo (jcgh@posta.unizar.es) winter, spring and summer were mostly localized and not generalized (both increase and decrease). Changes in PCI seem to be complex and appear to be related to global atmospheric features and synoptic and local factors affecting precipitation trends. We discuss the possible explanation linked to the atmospheric pattern and monthly trends and their implications.

The main characteristic of landscape evolution in the Pyrenees during the 20th century is the increased presence of shrubs in old fields. Revegetation is mainly recorded on medium and low slopes because of land abandonment. The increase in shrubs causes the loss of grazing resources during winter, landscape homogenization and an increase in fire risk. The objective of this paper was to create a scenario for land use change by combining Geographical Information Systems (GIS) and Landscape Ecology Analysis (LEA). To improve the present seasonal imbalance in pastoral resources, the scenario proposes to convert shrubland areas to grasslands without an excessive increase in soil erosion or landscape fragmentation. The results obtained indicate that the strategy produces greater landscape diversity and an increase in annual pasture resources (16.7%), which exceeds 60% of total in winter. The effects of landscape fragmentation on biodiversity, fire risk control and the imbalance of pastures are discussed. The scenario would improve extensive livestock farming, which is the most important economic activity in this area and other Mediterranean mountains.