Spatially-distributed IDF curves for Center-Southern Chile using IMERG

<p>The Intensity-Duration-Frequency (IDF) curves are crucial for urban drainage design and to mitigate the impact of extreme precipitation events and floods. However, many regions lack a high-density network of rain gauges to adequately characterise the spatial distribution of precipitation events. In this work we compute IDF curves for the South-Central Chilean region (26-56°S) using the latest version of the Integrated Multi-satellitE Retrievals for GPM (IMERGv06B) for 2001-2018, with a spatial resolution of 0.10° and half-hourly temporal frequency.</p><p><br>First, we evaluated the performance of IMERGv06B against 344 rain gauge stations at daily, monthly and annual temporal scales using a point-to-pixel approach. The modified Kling-Gupta efficiency (KGE’) and its components (linear correlation, bias, and variability ratio) were selected as continuous indices of performance. Secondly, we fit maximum precipitation intensities from 14 long-term rain gauge stations to three probability density functions (Gumbel, Log-Pearson Type III, and GEV II) to evaluate: i) the impact of using 15-year rainfall time series in the computation of IDF curves instead of using the typical long-term periods (~ 30 years); and ii) to select the best distribution function for the study area. The Gumbel distribution was selected to obtain the maximum annual intensities for each grid-cell within the study area for 12 durations (0.5, 1, 2, 4, 6, 8, 10, 12, 18, 24, 48, and 72 h) and 6 return periods (T=2, 5, 10, 25, 50, and 100 years).</p><p><br>The application of the Wilcoxon Mann-Whitney test indicates that differences between IDF curves obtained from 15 years of records at the 14 long-term rain gauges and those derived from 25 years of record (or more) are not statistically significant, and therefore, 15 years of record are enough (although not optimal) to compute the IDF curves. Also, our results show that IMERGv06B is able to represent the spatial distribution of precipitation at daily, monthly and annual temporal scales over the study area. Moreover, the obtained precipitation intensities showed high spatial variability, mainly over the Near North (26.0-32.2°S) and the Far South (43.7-56.0°S). Additionally, the intensities from Central Chile (32.2-36.4°S) to the Near South (36.4-43.7°S) were systematically higher compared to the intensities described in older official governmental reports, suggesting an increase in precipitation intensities during recent decades.</p>

Observations of Extreme Short-Term Precipitation Associated with Supercells and Mesovortices

Extreme hourly rainfall accumulations (e.g., exceeding 75 mm h−1) in several noteworthy flash flood events have suggested that the most intense accumulations were attendant with discrete mesoscale rotation or rotation embedded within larger organized systems. This research aims to explore how often extreme short-term rain rates in the United States are associated with storm-scale or mesoscale vortices. Five years of METAR observations and three years of Stage-IV analyses were obtained and filtered for hourly accumulations over 75 and 100 mm, respectively, clustered into events, and subjectively identified for rotation. The distribution of the short-term, locally extreme events shows the majority of the events were located along the Atlantic and Gulf of Mexico coastlines with additional events occurring in the central plains and into the Midwest. Nearly 50% of the cases were associated with low-level rotation in high-precipitation supercells or mesoscale vortices embedded in organized storm modes. Rotation events occurred more clearly in the warm sector, while nonrotation events tended to occur along a surface boundary. The rotation events tended to produce higher hourly accumulations over a larger region, but were associated with somewhat stronger synoptic-to-mesoscale forcing for ascent and more total column moisture. These results support recent modeling results suggesting that rotationally induced dynamic vertical pressure perturbations should not be ignored when it comes to extreme precipitation and can potentially enhance the short-term rain rates.

SISTEM INFORMASI GEOGRAFIS WILAYAH RAWAN BANJIR DI KOTA PEKANBARU

Based on the geographical location of Pekanbaru City is one of the areas included in flood-prone areas, even said that the city of Pekanbaru is included in the red zone related to flooding, seeing from the majority of the existing area is the rawah and river banks. The National Flood Mitigation Agency (BNPB) noted that the city of Pekanbaru is one of the flood-prone cities on the island of Sumatra. In addition to determining flood-prone areas for the Regional BPBD Office in Pekanbaru City, the community also wants to know the location that often floods and determine the long-term rain intensity capacity that will cause flooding, so that it does not hinder the daily activities. To deal with this problem, a Geographical Information System needs to be developed that can determine areas that often occur in natural flooding. Geographical information systems are expected to be able to assist the BPBD Office in managing flood data that has occurred in the city of Pekanbaru, and help provide information about floods that are needed by the community to anticipate further flood events.

Representative rainfall thresholds for flash floods in the Cali river watershed, Colombia

In the 21st century, societies face a significant increase in the number of extreme hydrometeorological events associated with climate variability (CV) and/or climate change (CC). Research has recently focused on establishing adaptation and mitigation measures to counteract the effects of CV and CC, especially those associated with precipitation, such as flash floods and flooding. In this study, 27 floods, listed in the historical database of natural disasters (DesInventar), occurring between 1980 and 2012, were analyzed. Using the daily hydrometeorological data, representative rainfall thresholds were defined to predict flash floods in the hydrographic basin of the Cali River, Colombia. Antecedent rainfall (AR), or short-term rain (1, 3, 5 and 7 days), and accumulated antecedent rainfall (AAR), or long-term rain (5, 7, 10, 15, 20, 25, 30, 60 and 90 days), levels were defined. The analysis showed that the greatest determinant for the occurrence of floods is AAR, with thresholds greater than 73, 95, 124, 170, 218 and 273 mm, for 5, 7, 10, 15, 20 and 25 days, respectively. Additionally, the data showed that, historically, the greatest number of flash floods (81.7 %) occurred in the Cali River basin in the months of April, May, and June.