Dendroclimatic signals in long tree-ring chronologies from the Himalayas of Nepal

We describe the development of a tree-ring chronology network in Nepal that is suitable for reconstructing temperature-related climate forcing over the past few hundred years. The network is composed of 32 tree-ring chronologies and is represented by five indigenous tree species. An empirical orthogonal function analysis of the chronologies over the common interval 1796-92 indicates the existence of coherent large-scale signals among the tree-ring chronologies that are hypothesized to reflect, in part, broad-scale climate forcing related to temperatures. A long monthly temperature record for Kathmandu is developed and used to test this hypothesis. In so doing, significant monthly and seasonal temperature responses are identified that provide guidance for the formal reconstruction of two temperature seasons: February-June (1546-91) and October-February (1605-91). Each reconstruction indicates the occurrence of unusually cold temperatures in 1815-22, which coincides with the eruption of Tambora in Indonesia. A novel method is also used to add probable missing multi-centennial temperature variance to each reconstruction. The resulting 'adjusted' reconstructions strongly reflect patterns of temperature variability associated with Little Ice Age cooling and warming into the 20th century, with the October-February season exhibiting the strongest increase in temperature over the past similar to400 years. Only the October - February season shows any evidence for late-20th century warming, whereas February-June temperatures have actually cooled since 1960 (as with the observational series). Copyright (C) 2003 Royal Meteorological Society.