Today, Northeastern India receives some of the highest annual rainfall totals globally. The major portion of annual precipitation in this region falls during the Indian Summer Monsoon season (June–September); however, this region also receives a significant amount of rainfall during the pre-monsoon season (March–May). Here, we quantitatively reconstruct the climate of the Upper Siwalik subgroup, eastern Himalayan region, based on fossil assemblages using the Coexistence Approach (CA). The age of the fossil assemblage is considered to be late Pliocene–early Pleistocene. Data reconstructed for the present-day and past pre-monsoon rainfall in Northeastern India indicate an increasing trend since the late Miocene–early Pliocene. During the late Pliocene–early Pleistocene (Upper Siwalik), the temperature seasonality between warm (27–28.1 °C) and cold months (22–23.6 °C) was less pronounced compared with present-day warm (27–27.7 °C) and cold (14.8–15.4 °C) months conditions at the fossil locality. The reconstructed rainfall data indicate a monsoonal type of climate having a strong seasonality in wet and dry seasons during the deposition of the Upper Siwalik sediments. Moreover, composition of the fossil floras and reconstructed palaeoclimate suggest a vegetation shift from dominantly wet evergreen to semi-evergreen at the fossil locality, coincident with an increase in length of the dry season. The comparison of reconstructed CA data and climate modelling data of a Gelasian time slice with that of previously reconstructed climate data by using Climate Leaf Analysis Multivariate Programme (CLAMP) analysis of the late Pliocene–early Pleistocene (Upper Siwalik) fossils of the same locality provides nearly the identical result. Furthermore, all the reconstructed data indicate a monsoonal type of climate during the deposition of the Upper Siwalik sediments.

今天，印度东北部的全球年度降雨量最高。该地区年降水量的主要部分在印度夏季风季节（6月至9月）。但是，该地区在季风前季节（3月至5月）也收到大量降雨。在这里，我们使用共存方法（CA）基于化石组合定量地重建了喜马拉雅东部地区上西瓦里克子群的气候。化石组合的年龄被认为是上新世晚期至早更新世。从印度中新世晚期至上新世早期以来，印度东北地区目前和过去季风前降雨的重建数据表明，这一趋势呈上升趋势。在上新世晚期至早更新世（上西瓦里克），温度季节在暖（27-28）之间。1°C）和寒冷月份（22–23.6°C）与化石所在地的当今温暖（27–27.7°C）和寒冷（14.8–15.4°C）月份相比不太明显。重建的降雨数据表明季风类型的气候在上西瓦里克沉积物的沉积过程中的干燥和潮湿季节具有强烈的季节性。此外，化石植物区系的组成和重建的古气候表明，化石地区的植被从占主导地位的湿性常绿植物向半常绿植物转变，与干旱季节长度的增加相吻合。通过使用气候叶分析多变量程序（CLAMP）分析同一地区晚期上新世-早更新世（上西瓦里克）化石，比较了格拉斯时间片的CA重建数据和气候建模数据与先前重建的气候数据的比较几乎相同的结果。此外，所有重建的数据都表明上西瓦里克沉积物的沉积是季风型气候。