RAINFALL VARIATIONS ALONG THE TEESTA VALLEY IN MOUNTAINOUS SLOPE OF SIKKIM

The mean weekly rainfall and iu rate oCchanee al Tadona and Ga~t. h ave been analysed toHJ: d ates of onset and withdrawal of southwest monsoon. The study attem pts to anal)'IC broad upecU oC raWaiVprecipitation di etributicn during th e four seaso ns. Th e importance oCorogra phy (or the rainfall in the mountainoUsvalley ha s been brought out. Th e study is based on da ta of 12 stations and of va ryina period of 4-25 yean.RainfaU over this mount ainous slope is found mono-modal with 8 maximum in Jul,...Aueult. Rainfall in thevalley shows sirikina: dilference in pa tterns even aLsho rt distance (4 km) and situated at a bieber altitude. Ra infallO~T station s in the valley increased up to 2000m esl and then decrease sharply. The central part ofthe valley with anaverage altitude of ISOQ.2000 m asl receives about 2~300 em of rainfall durina aouthwest monsoon season

Quantifying recent lake level changes in Patagonia (Argentina and Chile): Back to the future?

<p>Lake levels in hydrologically closed-basins are very sensitive to climatically and/or anthropogenically triggered environmental changes. Their record through time can provide valuable information to forecast changes that can have substantial economical and societal impact.</p><p>Increasing precipitation in eastern Patagonia (Argentina) have been documented following years with strong El Niño (cold) events using historical and meteorological data. Quantifying changes in modern lake levels allow determining the impact of rainfall variations while contributing to anticipate the evolution of lacustrine systems over the next decades with expected fluctuations in ENSO frequencies. Laguna Carrilaufquen Grande is located in the intermontane Maquinchao Basin, Argentina. Its dimension fluctuates greatly, from 20 to 55 km<sup>2</sup> water surface area and an average water depth of 3 m. Several well-preserved gravelly beach ridges witness rainfall variations that can be compared to meteorological data and satellite images covering the last ~50 years. Our results show that in 2016 lake level was the lowest of the past 44 years whereas the maximum lake level was recorded in 1985 (+11.8 m above the current lake level) in a position 1.6 km to the east of the present shoreline. A five-years moving average rainfall record of the area was calculated smoothing the extreme annual events and correlated to the determined lake level fluctuations. The annual variation of lake levels was up to 1.2 m (e.g. 2014) whereas decadal variations related to humid-arid periods for the interval 2002 to 2016 were up to 9.4 m. These data are consistent with those from other monitored lakes and, thus, our approach opens up new perspectives to understand the historical water level fluctuations of lakes with non-available monitoring data.</p><p> </p><p>Laguna de los Cisnes in the Chilean section of the island of Tierra del Fuego, is a closed-lake presently divided into two sections of 2.2 and 11.9 km<sup>2</sup>, respectively. These two water bodies were united in the past forming a single larger lake. The lake level was  ca. 4 m higher than today as shown by clear shorelines and the outcropping of large Ca-rich microbialites. Historical data, aerial photographs and satellite images indicate that the most recent changes in lake level are the result of a massive decrease of water input during the last half of the 20<sup>th</sup> century triggered by an indiscriminate use of the incoming water for agricultural purposes. The spectacular outcropping of living and fossil microbialites is not only interesting from a scientific point of view but has also initiated the development of the site as a local touristic attraction. However, if the use of the incoming water for agriculture in the catchment remains unregulated the lake water level might drop dangerously and eventually the lake might fully desiccate.</p><p>These two examples illustrate how recent changes in lake level can be used to anticipate the near future of lakes. They show that ongoing climate changes along with the growing demand of natural resources have already started to impact lacustrine systems and this is likely to increase in the decades to come.</p>

Tropical Rainfall Variability Accompanying Global Normal Mode Oscillations

Using global precipitation datasets (GSMaP, TRMM) and the latest reanalysis data (ERA5) we performed a comprehensive analysis of the tropical rainfall variability that accompanies global-scale, low-frequency normal modes: Rossby, Rossby-gravity and Kelvin modes. Cross spectral analysis and lag-regression analysis both showed that coherent rainfall variations accompany not only the wavenumber 1 gravest Rossby mode (“5 day” wave) but other low-frequency modes. The normal mode rainfall variations are enhanced in regions such as the Amazon basin, but also include circumglobally travelling structures with substantial amplitude over the open ocean. These results are remarkably consistent among the three datasets including even ERA5 rainfall data. The circumglobal rainfall signals may be considered primarily as a response to the normal mode dynamical variations. We found that the phase relationship between rainfall and dynamical field variability is strongly dependent on the type of mode and even on the zonal wavenumber. We suggest that this is explained by the difference in relative importance of two underlying processes: (1) moisture-flux convergence and (2) rainfall enhancement associated with adiabatic cooling. Our determined rainfall signals are the response to quasi-monochromatic, periodic waves that have a simple vertical structure and represent one special case of tropospheric wave-rainfall coupling. Implications for the mechanism of 12-hr rainfall oscillations believed to be forced by the atmospheric tide are also considered.

Assessment of Near-Real-Time Satellite Precipitation Products from GSMaP in Monitoring Rainfall Variations over Taiwan

This study assessed four near-real-time satellite precipitation products (NRT SPPs) of Global Satellite Mapping of Precipitation (GSMaP)—NRT v6 (hereafter NRT6), NRT v7 (hereafter NRT7), Gauge-NRT v6 (hereafter GNRT6), and Gauge-NRT v7 (hereafter GNRT7)— in representing the daily and monthly rainfall variations over Taiwan, an island with complex terrain. The GNRT products are the gauge-adjusted version of NRT products. Evaluations for warm (May–October) and cold months (November–April) were conducted from May 2017 to April 2020. By using observations from more than 400 surface gauges in Taiwan as a reference, our evaluations showed that GNRT products had a greater error than NRT products in underestimating the monthly mean rainfall, especially during the warm months. Among SPPs, NRT7 performed best in quantitative monthly mean rainfall estimation; however, when examining the daily scale, GNRT6 and GNRT7 were superior, particularly for monitoring stronger (i.e., more intense) rainfall events during warm and cold months, respectively. Spatially, the major improvement from NRT6 to GNRT6 (from NRT7 to GNRT7) in monitoring stronger rainfall events over southwestern Taiwan was revealed during warm (cold) months. From NRT6 to NRT7, the improvement in daily rainfall estimation primarily occurred over southwestern and northwestern Taiwan during the warm and cold months, respectively. Possible explanations for the differences between the ability of SPPs are attributed to the algorithms used in SPPs. These findings highlight that different NRT SPPs of GSMaP should be used for studying or monitoring the rainfall variations over Taiwan for different purposes (e.g., warning of floods in different seasons, studying monthly or daily precipitation features in different seasons, etc.).

Elevation Dependence of the Impact of Global Warming on Rainfall Variations in a Tropical Island

Due to their vulnerability, understanding the impacts of global warming on rainfall is important for a tropical country and islands. This research aimed to assess the impact of global warming on rainfall in Madagascar, using the Mann-Kendall test, continuous wavelet transform, and polynomial regression. The result showed that the annual, seasonal maximum, and minimum temperature increased, while elevation amplified the increase of maximum temperature. Different trends in rainfall were found in the 22 regions of Madagascar but in general, the increasing trend in rainfall was prominent at a higher elevation than lower elevation. The annual rainfall decreased up to −5 mm per year for the regions located below 450 m of altitude while increased up to +5 mm per year above 500 m. We found that the wet becomes wetter with an important increase in rainfall in summer and the increase in temperature influenced the rainfall. The annual rainfall increased with temperature and elevation. However, if the increase in temperature was more than 0.03 °C per year, the annual rainfall increased regardless of elevation. The knowledge of the elevation dependence of the impact of warming on rainfall is important for water resources management and climate change adaptation strategies, especially for island nations and African countries.

Subseasonal prediction performance for austral summer South American rainfall

Skilful and reliable predictions of week-to-week rainfall variations in South America, two to three weeks ahead, are essential to protect lives, livelihoods and ecosystems. We evaluate forecast performance for weekly rainfall in extended austral summer (November–March) in four contemporary subseasonal systems, including a new Brazilian model, at 1–5 week leads for 1999–2010. We measure performance by the correlation coefficient (in time) between predicted and observed rainfall; we measure skill by the Brier Skill Score for rainfall terciles against a climatological reference forecast. We assess unconditional performance (i.e., regardless of initial condition) and conditional performance based on the initial phase of the Madden–Julian Oscillation (MJO) and the El Niño–Southern Oscillation (ENSO). All models display substantial mean rainfall biases, including dry biases in Amazonia and wet biases near the Andes, which are established by Week 1 and vary little thereafter. Unconditional performance extends to Week 2 in all regions except for Amazonia and the Andes, but to Week 3 only over northern, northeastern and southeastern South America. Skill for upper- and lower-tercile rainfall extends only to Week 1. Conditional performance is not systematically or significantly higher than unconditional performance; ENSO and MJO events provide limited “windows of opportunity” for improved S2S predictions that are region- and model-dependent. Conditional performance may be degraded by errors in predicted ENSO and MJO teleconnections to regional rainfall, even at short lead times.

Study of historical precipitation series from 1988 to 2019 in the city of Francisco Beltrão-PR

It is through rainwater that water sources are recharged and subsequently distributed to the population, which uses this water in different ways. Knowledge of rainfall variations is of great importance for the planning and management of water resources, such as the study of intense and dry rainfall. This study aimed to analyze the historical series of rainfall from 1988 to 2019 in the city of Francisco Beltrão - PR, northwest region of the state of Paraná. As a methodology, annual precipitation data were taken, which is measured by monthly rainfall averages, on the website Águas Paraná Paraná), and with this information, it was possible to carry out analyzes of rainfall in the interval of thirty years, which is the minimum time. necessary to observe significant changes in the climate. From the results found and the analysis of the historical series, it was observed that the years 1988 and 1990 had the lowest (108 rainy days) amount of precipitation and the highest (173 rainy days), respectively. The big difference between them is that in 1988 Brazil was under the influence of the La Niña phenomenon, which reduces the rainfall regime. In addition, it was noted that there was a considerable increase in precipitation, which raises the hypothesis of the expansion of pollution, which consequently increases the rate of evapotranspiration and thus leads to an increase in rainy days. In the studied timeframe, Francisco Beltrão expanded his industrial area, which, consequently, may have generated greater atmospheric emissions. Thus, it was possible to conclude that from 1988 to 2019 the rainfall regime increased, assuming the greatest amount of pollution. There were also years when El Niño and La Ninã acted more intensely, causing disturbances that directly affected agriculture and vegetation.