**Nguyen Tien Thanh**

Department of Hydro-meteorological Modeling and Forecasting, Thuyloi University, 175 Tay Son, Dong Da, Hanoi, Vietnam; thanhnt@tlu.edu.vn

Received: 23 August 2018; Accepted: 18 September 2018; Published: 20 September 2018

**Abstract:** This study presents a method to investigate meteorological drought characteristics using multiple climate models for multiple timescales under two representative concentration pathway (RCP) scenarios, RCP4.5 and RCP8.5, during 2021–2050. The methods of delta change factor, unequal weights, standardized precipitation index, Mann–Kendall and Sen's slope are proposed and applied with the main purpose of reducing uncertainty in climate projections and detection of the projection trends in meteorological drought. Climate simulations of three regional climate models driven by four global climate models are used to estimate weights for each run on the basic of rank sum. The reliability is then assessed by comparing a weighted ensemble climate output with observations during 1989–2008. Timescales of 1, 3, 6, 9, 12, and 24 months are considered to calculate the standardized precipitation index, taking the Vu Gia-Thu Bon (VG-TB) as a pilot basin. The results show efficient precipitation simulations using unequal weights. In the same timescales, the occurrence of moderately wet events is smaller than that of moderately dry events under the RCP4.5 scenario during 2021–2050. Events classified as "extremely wet", "extremely dry", "very wet" and "severely dry" are expected to rarely occur under the RCP8.5 scenario.

**Keywords:** multiple climate models; standardized precipitation index (SPI); droughts; weights; Vu Gia-Thu Bon
