Analysis of Rain Types and Their Z–R Relationships at Different Locations in the High Andes of Southern Ecuador

Abstract

Information on the spatiotemporal rainfall occurrence, its microphysical characteristics, and its reflectivity–rainfall (Z–R) relations required to provide rainfall mapping based on rain radar data is limited for tropical high mountains. Therefore, this study aims to analyze rainfall types in the Andes cordillera to derive different rain-type Z–R relations using disdrometer observations at three study sites representative for different geographic positions and elevations (2610, 3626, and 3773 m MSL). Rain categorization based on mean drop volume diameter (Dm) thresholds [0.1 < Dm (mm) ≤ 0.5; 0.5 < Dm (mm) ≤ 1.0; 1.0 < Dm (mm) ≤ 2.0] was performed using drop size distribution data at a 5-min time step over an approximate 2-yr period at each location. The findings are as follows: (i) Rain observations characterized by higher (lower) Dm and rain rates are more frequent at the lower (higher) site. (ii) Because of its geographic position, very light rain (drizzle) is more common at higher altitudes with longer-duration events, whereas rainfall is more convective at the lower range. (iii) The specific spatial exposition regarding cloud and rain formation seems to play an important role for derivation of the local Z–R relationship. (iv) Low A coefficients (≤60) for the first rain type resemble typical characteristics of orographic precipitation. (v) Greater values of A (lowest and highest stations for Dm > 1.0 mm) are attributed to transitional rainfall as found in other studies. (vi) Rain-type Z–R relations show a better adjustment in comparison with site-specific Z–R relationships. This study is the first contribution of Z–R relations for tropical rainfall in the high Andes.

Precipitation Characteristics at Two Locations in the Tropical Andes by Means of Vertically Pointing Micro-Rain Radar Observations

“…With the two year MRR datasets from Cuenca and Huaraz, we were able to analyze the occurrence and duration of precipitation events, as well as the temporal evolution of precipitation with respect to rain rates, radar reflectivities, fall velocities, and drop size distributions. The number and durations of the events in Cuenca are consistent with the study from Orellana-Alvear et al [14], who analyzed these parameters using disdrometer data from March 2015 to August 2016. Our results also show that both sites have more events with higher precipitation intensity during the daytime.…”

“…The climate is characterized by a bimodal rainfall pattern with two wet seasons (MAM and SON). Cuenca has a mean annual precipitation of 969 mm [14] and a mean temperature of 14 • C [29].…”

Flash-Flood Forecasting in an Andean Mountain Catchment—Development of a Step-Wise Methodology Based on the Random Forest Algorithm

“…As a result, convective and orographic cloud formations occurs [31]. Although precipitation (in terms of volume) mainly falls as drizzle (≈1 mm/h), higher intensity events are also experienced in the catchment (up to 140 mm/h) [32,33].…”

Rainfall Estimates with Respect to Rainfall Types Using S-Band Polarimetric Radar in Korea

“…Equations (13) and (14) were used for retrieving D 0 and N w from the observed Z H and Z DR . Equation (15) was used for classification: If the retrieved logN w is greater (smaller) than that given by this equation, the pixel is assigned as convective (stratiform) rain (hereafter the DSD-based method).…”

“…Alvear et al [13] derived different rain-type Z-R relations using disdrometer data observed at three different geographic and height based on mean drop volume diameter thresholds in the high Andes of southern Ecuador. Alvear et al [14] proposed random forest model (FM) to get more accurate rainfall amounts using X-band radar installed on the highest mountain in the world.…”