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Abstract. The sensitivity of chemical weathering to climatic and erosional forcing is well established at regional scales. However, soil formation is known to vary strongly along catenas where topography, hydrology, and vegetation cause differences in soil properties and, possibly, chemical weathering. This study applies the SoilGen model to evaluate the link between the topographic position and hydrology with the chemical weathering of soil profiles on a north–south catena in southern Spain. We simulated soil formation in seven selected locations over a 20 000-year period and compared it against field measurements. There was good agreement between simulated and measured chemical depletion fraction (CDF; R2=0.47). An important variation in CDF values along the catena was observed that is better explained by the hydrological variables than by the position along the catena alone or by the slope gradient. A positive trend between CDF data and soil moisture and infiltration and a negative trend with water residence time was found. This implies that these hydrological variables are good predictors of the variability in soil properties. The model sensitivity was evaluated with a large precipitation gradient (200–1200 mm yr−1). The model results show an increase in the chemical weathering of the profiles up to a mean annual precipitation value of 800 mm yr−1, after which it drops again. A marked depth gradient was obtained for CDF up to 800 mm yr−1, and a uniform depth distribution was obtained with precipitation above this threshold. This threshold reflects a change in behaviour, where the higher soil moisture and infiltration lead to shorter water transit times and decreased weathering. Interestingly, this corroborates similar findings on the relation of other soil properties to precipitation and should be explored in further research.

Crop yield prediction considering soil moisture as a proxy for water supply remains crucial for global food security. This study evaluates the potential of using seasonal weather forecasts combined with a drought index, Static Stress, based on both precipitation and soil moisture conditions to predict winter wheat yield 7 to 1 month in advance in Córdoba (South Spain). First, using observed climate and crop yield data we evaluate the use of Static Stress, as a potential crop yield predictor and compare it to a more traditionally used index, the SPEI, which is only based on precipitation conditions. Then we evaluate the performance of simple linear regression models to predict crop yields from forecasted Static Stress values calculated using weather forecast data from the ECMWF seasonal forecasting system (SEAS5). We find that Static Stress is better correlated to crop yield than SPEI and that Static Stress derived from seasonal forecasts has a good performance (R2 > 0.5; p-value < 0.05) for crop yield predictions of 4 or fewer months before harvest, i.e., from March to July. In this case study, these results indicate that drought indicators that consider soil moisture conditions are better predictors of crop yields than indicators that only consider precipitation. Furthermore, this study demonstrates the potential of using simple regression models together with mid-term forecasts of the Static Stress index to maximize cereal yields and mitigate drought impacts.

Abstract. The sensitivity of chemical weathering to climatic and erosional forcing is well established at regional scales. However, soil formation is known to vary strongly along catenas where topography, hydrology, and vegetation cause differences in soil properties and possibly chemical weathering. This study applies the SoilGen model to evaluate the link between topographic position and hydrology with the chemical weathering of soil profiles on a north-south catena in southern Spain. Pedogenesis was measured and simulated in seven selected locations over a 20000-year period. A good correspondence between simulated and measured chemical depletion fraction (CDF) was obtained (R2 = 0.47). An important variation in CDF values along the catena was observed, although the position along the catena alone, nor by the slope gradient, explained this variation well. However, the hydrological variables explained the observed trends better. A positive trend between CDF data and soil moisture and infiltration and a negative trend with water residence time was found. The model sensitivity was evaluated with a large precipitation gradient (200–1200 mm yr−1). While a marked depth gradient was obtained for CDF with precipitation up to 800 mm yr−1, a uniform depth distribution was obtained with precipitation above 800 mm yr−1. The basic pattern for the response of chemical weathering to precipitation is a unimodal curve, with a maximum around a mean annual precipitation value of 800 mm yr−1. Interestingly, this corroborates similar findings on the relation of other soil properties to precipitation and should be explored in further research.

Purpose The use of fallout radionuclides as proxies for the study of soil redistribution processes in semiarid environments of Southern Spain has been restricted to 137Cs. The potential and limitations of alternative proxies such as 239+240Pu and 210Pbxs should be explored given the expected constrains imposed by the features of the study area. Materials and methods Four soil and one sediment cores were collected in a highly eroded area to test the feasibility of these proxies under demanding conditions. The use of gamma spectrometry and ICP-MS did allow exploring the potential of 210Pbxs and Pu isotopes against the well-established tracer, 137Cs. The activity ratios 239+240Pu/137Cs were explored to evaluate the previous evolution of the sampling sites. Soil redistribution rates were estimated using the model MODERN. Results and discussion Despite all the profiles showed intense perturbation, Pu isotopes showed the highest potential thanks to higher sensitivity and sample throughput. The deviations of 239+240Pu/137Cs inventory ratios (0.012–0.158) from the global fallout average (0.026 ± 0.003) suggest that the sediment core was a deposition site involving alternate episodes of topsoil removal and incorporation from different sources. The calculated erosion rates ranged 34–43 t ha−1 year−1, being in good agreement for 137Cs and 239+240Pu. 210Pbxs was not used due to low-quality data. Conclusions The use of Pu as a tracer of soil redistribution processes in semiarid areas seems to be promising even under severe erosion conditions. The use of 210Pbxs is not recommended in this area due to its low concentration. Graphical Abstract