Watering ponds are an important source of drinking water supply for livestock in semi-arid rangelands. Understanding the hydrological functioning of this kind of infrastructures is crucial for efficient water management in areas where water resources are often scarce. In this line, we have analyzed temporal patterns of water availability in a set of watering ponds located in Iberian rangelands and their relationship with temporal rainfall variability. In addition, the effectiveness of the ponds for conserving stored water during dry periods and some influencing factors (pond size and catchment area) have also been assessed. The results showed a high correlation between water availability and precedent rainfall, confirming, on the one hand, the capacity of storage of these infrastructures and, on the other hand, the importance of temporal rainfall patterns in their hydrological behavior. Our findings point to a minimum pond area of 2000 m2 and a catchment area/storage capacity ratio around 100 m−1 in order for watering ponds can face the dry summer period with certain guarantees, at least in regular hydrological years. Nonetheless, the vulnerability shown by the majority of the watering ponds in times of drought limits their usefulness as unique sources of water supply in many farms.

No abstract

Watering ponds represent an important part of the hydrological resources in some water-limited environments. Knowledge about their storage capacity and geometrical characteristics is crucial for a better understanding and management of water resources in the context of climate change. In this study, the suitability of different geomatic approaches to model watering pond geometry and estimate pond-specific and generalized volume–area–height (V–A–h) relationships was tested. Terrestrial structure-from-motion and multi-view-stereo photogrammetry (SfM-MVS), terrestrial laser scanner (TLS), laser-imaging detection and ranging (LIDAR), and aerial SfM-MVS were tested for the emerged terrain, while the global navigation satellite system (GNSS) was used to survey the submerged terrain and to test the resulting digital elevation models (DEMs). The combined use of terrestrial SfM-MVS and GNSS produced accurate DEMs of the ponds that resulted in an average error of 1.19% in the maximum volume estimation, comparable to that obtained by the TLS+GNSS approach (3.27%). From these DEMs, power and quadratic functions were used to express pond-specific and generalized V–A–h relationships and checked for accuracy. The results revealed that quadratic functions fit the data particularly well (R2 ≥ 0.995 and NRMSE < 2.25%) and can therefore be reliably used as simple geometric models of watering ponds in hydrological simulation studies. Finally, a generalized V–A power relationship was obtained. This relationship may be a valuable tool to estimate the storage capacity of other watering ponds in comparable areas in a context of data scarcity.

&lt;p&gt;Watering ponds are the main source of drinking water supply for livestock in the rangelands of the SW Iberian Peninsula. Most of these ponds consist of small earth dams which collect surface runoff from intermittent streams, with pond sizes rarely exceeding 1 ha. Understanding the hydrological functioning of this type of infrastructures is crucial for an efficient water management in extensive livestock farms, especially in semi-arid areas, where water resources are often scarce.&lt;/p&gt;&lt;p&gt;In this line, we have analysed the temporal patterns of water availability in a sample of representative livestock watering ponds in the SW Iberian Peninsula, being the objectives (1) to determine the influence of temporal rainfall variability on water availability in the ponds; (2) to examine the influence of factors such as pond size and catchment area on the effectiveness of the ponds, understood as their capacity to keep water during dry periods; and (3) to suggest minimum values for those factors, which can serve as a guide for the design of watering ponds in comparable rangeland areas. The applied methodology was primarily based on the analysis of aerial photographs and rainfall data available from public sources, requiring only few field measurements, and could therefore be used in areas with data scarcity.&lt;/p&gt;&lt;p&gt;High correlation coefficients were obtained between the water availability observed in the ponds and the antecedent rainfall at several time scales, evidencing the principal role of precipitation in the hydrological dynamics of these infrastructures in the study area. The accumulation periods (AP) of antecedent rainfall that best explained the hydrological response of the ponds depended largely on pond size. In those ponds whose maximum flooded area (A&lt;sub&gt;max&lt;/sub&gt;) was less than 2000 m&lt;sup&gt;2&lt;/sup&gt;, water availability in the ponds was greatly influenced by AP between 2 and 5 months, while for the ponds larger than 2000 m&lt;sup&gt;2&lt;/sup&gt;, the best correlations were obtained for AP greater than 6 months. These results highlight the key role of the size of the ponds in their effectiveness. Thus, since the dry season usually lasts in the study area for 3-4 months, the large ponds (A&lt;sub&gt;max&lt;/sub&gt; &gt; 2000 m&lt;sup&gt;2&lt;/sup&gt;) could remain operational throughout the summer, if it rains enough during the wet season and if their watersheds are large enough to allow a sufficiently high pond water level to be reached at the end of the wet season. In relation to the latter, the analyses carried out led us to suggest, for the study area, a minimum value of the catchment-area/pond-capacity ratio around 100 m&lt;sup&gt;-1&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;Moreover, the analysis of the water availability observed in the ponds under drought conditions (i.e., with an antecedent rainfall substantially lower than normal for the corresponding time of year) revealed a high vulnerability to droughts in most of the ponds, which limits their use as the sole source of water supply in many farms.&lt;/p&gt;