Small-scale farmers in the Rio Santa basin in the Peruvian Andes see their tradi-
tional way of rain-fed agriculture threatened by climate change. In the mountainous
terrain, rain gauge measurements are too scarce to confirm the farmers perceptions
of precipitation-related changes in the past decades. Reanalysis datasets provide the
opportunity to investigate area-wide whether climatic conditions have changed. The
aim of this thesis was to find the most suitable reanalysis dataset to then determine
whether and how agriculturally relevant climate variables have changed in the past.
For this purpose, I compared different reanalyses with rain gauge measurements
by analysing the reanalyses’ skill in reproducing certain precipitation features and
by statistical measures like Pearson correlation.
ERA5-Land showed the best performance and has the best spatial resolution.
It was therefore selected to be examined for changing frequencies of occurrence of
certain climate metrics per year. It was found that the number of frost days and the
mean annual temperature increased significantly in many parts of the study region
during the last four decades. Changes in precipitation are region-dependent: The
northern part of the Rio Santa basin experienced a significant increase in annual
precipitation with less precipitation days but more heavy precipitation days. In the
eastern surrounding region annual precipitation as well as the number of precipita-
tion days and the number of heavy precipitation days decreased significantly.
I discuss data and model uncertainties and fundamental assumptions made
when selecting ERA5-Land as proxy data. Furthermore, I discuss how changes in
the frequency of occurrence of climate metrics affect small-scale farmers and which
assumptions were made when developing the agriculturally relevant metrics.
I conclude that ERA5-Land can reliably be used as proxy data for precipitation
in the Rio Santa basin. Furthermore I find that climate change has the potential to
have both a positive and a negative impact on small-scale agriculture in the basin.
On the one hand, warmer temperatures are generally beneficial for crop growth and
a reduction in frost days may allow cultivation at higher altitudes. On the other
hand, in some locations the potential danger associated with heavy precipitation
events has increased while in others water scarcity has increased. In conclusion,
farmers’ perceptions of precipitation changes were partially reflected in this study.