Widespread greening suggests increased dry-season plant water availability in the Rio Santa valley, Peruvian Andes

Changing water availability is making climate change tangible and is often a great concern for affected societies. In rural settings of the global south where the livelihood of many people relies on subsistence-based agriculture, changes in seasonality of climate variables or increasing weather extremes can have far-reaching consequences including rural exodus and increase of poverty and vulnerability. The slopes of the Rio Santa basin, located in the Peruvian Andes, are home to many farmers whose livelihoods have already been increasingly challenged by economical and societal developments in the past decades. The local agriculture is mostly rain-fed and plant-growth is determined by the appearance of seasonal rainfalls which are occurring during an annual cycle of a distinct wet and dry season.

Recently, farmers reported that they are facing changed timing and intensities of seasonal rainfalls with detrimental effects on crop yields. These reports were not supported by analysis of historical meteorological records in previous research, but there remains considerable uncertainty regarding the quality of the data. To overcome this, we exploited 20 years of satellite-derived vegetation greenness data as a proxy for water availability. In comparison to the analysed rainfall products, these data are available in unpreceded spatio-temporal resolution and allowed us to gain new insights into recent trends and changes in the variability of plant available water.

We confirmed that no clear conclusion can be drawn from several rainfall datasets but we find a significant increase of plant greenness in the Rio Santa basin, particularly pronounced during the dry season. This indicates an overall increase of plant available water over the past two decades. In agreement to these greening patterns, we found a delayed end of the growing season which either implies a later retreat of the seasonal rainfalls or larger amounts of rainfall during the wet season feeding storages of the hydrological system. The start of the growing season, however, fluctuates highly from year to year with variation of up to two months, governing the overall growing season length. This variability is likely linked to the perception of local farmers, as it hampers the planning of sowing dates and overall complicates successful farming.


Science Flash Hänchen

The ridgelines display the variability in timing of the growing season for each of the 20 growing seasons between 2000 and 2020. A smaller width of the distribution can be interpreted as plant growth in the Rio Santa basin being temporally more uniformly, while a larger width shows larger deviations of the timing. Additionally, the plot displays the large interannual variability of the start of the growing season and the increasingly delayed end of the growing season.

Hänchen, L., Klein, C., Maussion, F., Gurgiser, W., Calanca, P., & Wohlfahrt, G. (2022). Widespread greening suggests increased dry-season plant water availability in the Rio Santa valley, Peruvian Andes. Earth System Dynamics 13(1): 595-611. DOI: https://doi.org/10.5194/esd-13-595-2022

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