Abstract
Study regionThe upper part of the Guayllabamba and Napo basins (78.2 ° W, 0.3 °S; 18,500 km2) in the equatorial Andes, which are vulnerable to stress on the ecosystem services. Study focusThis paper analyses the diurnal cycle of precipitation over a transect from the Andes to the Amazon. The diurnal cycle is estimated as the diurnal distribution of precipitation for 2014–2019 using records from 80 stations. Cluster analysis performed on the diurnal cycle estimates depicts the spatial association between the diurnal and seasonal cycles of precipitation. New hydrological insightsA northwest-southeast spatial variation in the diurnal and seasonal cycles is identified with four groups of stations. In the western part, the seasonal cycles of Groups 1 and 2 are bimodal with precipitation maxima in the March-April and October-November seasons and a short drier season in July-August. In the eastern part, Group 3 also presents bimodality, but a weaker seasonal cycle. Conversely, Group 4 is unimodal with a peak in June. Distinct diurnal cycles are observed in both drier and wetter seasons of Groups 1–3; no marked diurnal cycle is observed in Group 4. Groups 3 and 4 are the most spatially heterogeneous, with an exceptional horizontal variation of 330 mm/yr/km. The analysis of these variations provides insight into the atmospheric dynamics driving precipitation in this zone, and may help to better optimize the water supply system.
Highlights
The diurnal cycle is the finest-scale regular mode of precipitation variability and is an essential aspect of local climate and the hydrological cycle
More recent research conducted in the Medellin Andean valley (6 ◦ N-6.6 ◦ N; Colombia) shows that the diurnal cycle is spatially coherent and varies seasonally depending on the life cycle of deep and large convective systems modulated at diurnal time scales (Bedoya et al, 2019)
We identified, for the first time, groups of stations varying spatially in the NW-SE direction over this region with complex topography which display concomitant diurnal and seasonal variations of precipitation
Summary
The diurnal cycle is the finest-scale regular mode of precipitation variability and is an essential aspect of local climate and the hydrological cycle. Precipitation variability in many cases is the major source of uncertainty in catchment hydrology (e.g., Beven, 2012; Buytaert et al, 2006) This is especially true in the high-altitude environments of the tropical Andes that provide essential ecosystem services like water storage and streamflow regulation for downstream water uses (Gonzalez-Zeas et al, 2019). Seasonal and west-east spatial variations of the Normalized Difference Vegetation Index (NDVI) have been identified in the Ecuadorian Andes and greening peaks are generally associated with lower rainfall (Haro-Carrion et al, 2021) To investigate such processes, fundamental knowledge about the diurnal variability of precipitation is required
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