Rainfall in the Andean Páramo: New Insights from High-Resolution Monitoring in Southern Ecuador

Abstract

In mountainous regions, rainfall plays a key role in water supply for millions of people. However, rainfall data for these sites are limited and generally of low quality, making it difficult to evaluate the nature, amount, and timing of rainfall. This is particularly true for the páramo, a high-elevation grassland in the northern Andes that is a primary source of water for large populations in Ecuador, Colombia, and Venezuela. In this study, high-resolution laser disdrometer data and standard tipping-bucket rain gauge data were used to improve knowledge of rainfall in the páramo. For 36 months, rainfall was monitored in a high-elevation (3780 m MSL) headwater catchment in southern Ecuador. Average annual rainfall during this period was 1345 mm. Results indicate that (i) when input from very low–intensity events (drizzle) is taken into account, rainfall is 15% higher than previously thought; (ii) rainfall occurs throughout the year (only approximately 12% of the days are dry); (iii) rainfall occurs primarily as drizzle (80% of rainfall duration), which accounts for 29% of total rainfall amount; and (iv) the timing and average intensity of rainfall varies throughout the year (shorter afternoon events are common from October to May, whereas longer night events—with lower intensities—are more frequent from June to September). Although some of these numbers may vary regionally, the results contribute to a better understanding of rainfall in the wet Andean páramo.

Effect of the Resolution of Tipping-Bucket Rain Gauge and Calculation Method on Rainfall Intensities in an Andean Mountain Gradient

“…In the CS method, according to the studies of Wang et al [22], Padrón et al [25] and Nystuen [41], the event definition is based on the maximum time lapse between two consecutive tips recorded by the TB rain gauge of 0.1 mm-resolution, and if the time lapse between them is 30 min or less they are considered to belong to the same event. For the TB rain gauges with different resolutions, the maximum time lapse of each one was determined as a linear relation of the definition mentioned above.…”

“…Lack of funding did not permit us to use a laser-optical disdrometer as a reference in each location along the altitudinal transect in this analysis. The Texas TB rain gauge compared to the laser-optical disdrometer showed an underestimation of the annual rainfall of 8% [25]. Further, the relationship between errors, altitude, and cumulative rainfall was examined.…”

Comparative Ground Validation of IMERG and TMPA at Variable Spatiotemporal Scales in the Tropical Andes

“…Because of the high frequency of low rainfall intensities in some parts of the tropical Andes (e.g., Padrón et al 2015), a threshold corresponding to one single record of the highest-resolution gauges available in the network (0.1 mm h 21 ) has been found to be suitable to assess the entire range of rainfall intensities without eliminating the lowest intensities or introducing assumptions as to their distribution. The empirical rainfall occurrence frequency (ROF) is expressed as…”

“…SPPs have also been shown to systematically overestimate low rainfall intensities (under 5 mm h 21 ), which occur frequently above 2000 m MSL (Derin et al 2016) and locally represent an important contribution to the total rainfall volume (Padrón et al 2015). Furthermore, there are regional differences in SPP performance depending on the principal sensor technology and the local rainfall properties as a result of interaction of the synoptic-scale climate processes with the complex topography (Derin et al 2016;Satgé et al 2016;Dinku et al 2010).…”

Insights into the water mean transit time in a high-elevation tropical ecosystem

“…Mean annual precipitation at the observatory is 1345 mm at 3780 m a.s.l. Precipitation shows low seasonality with two relatively drier months (August and September) and primarily falls as drizzle (Padrón et al, 2015). Mean annual temperature is 6.0 • C at 3780 m a.s.l.…”