The Global Historical Climatology Network Monthly Precipitation Dataset, Version 4

Abstract

The Global Historical Climatology Network (GHCN) monthly precipitation dataset contains historical time series for thousands of land surface stations worldwide. Initially released in 1992 and revised in 1998, the dataset has been employed in a variety of applications over the past three decades, including operational monitoring, applied research, and international assessments. This paper describes the data and methods used to compile the latest edition (version 4), which has three major enhancements. The first enhancement is to the station network, which increased in size by a factor of five due to the inclusion of dozens of new source datasets, most notably GHCN Daily (GHCNd). The second improvement is the application of a rule-based algorithm to compare and merge records representing the same location. The third enhancement is to the quality assurance approach, now consisting of 18 new checks based on GHCNd and other operational systems. Updated monthly, the resulting dataset consists of time series of monthly precipitation totals at more than 120,000 worldwide stations, including more than 33,000 active observing sites.

Fig. 1

This collection of four tables shows how the four station matching tests come together to adjudicate station pairs. Symbols for distance and data matches indicate if the two records were equivalent (=), similar (≈), inconclusive (?), or different (≠). Since a station name match requires the stations to be within 100 km of each other, there can be no outcomes of inconclusive or mismatched distances in the upper tables. Descriptions of the five outcome sets of strong match (S, green), fair match (F, yellow), neutral (N, gray), conflicting (C, red), and distinct (D, blue) are given in Table 2.

Fig. 2

The number of monthly values in GMP4 (black) and GMP2 (red) for the world excluding the US (solid) and the US only (dashed).

Fig. 3

Depictions of the average number of monthly values per year within each 5-degree box for different blocks of years (1850–1899, 1900–1949, 1950–1999, 2000–2019) and for GMP2 vs GMP4. The scale is increasing dark shades of green, with every two increments corresponding to a power of 10.

Fig. 4

Locations compared between GMP2 and GMP4. Green triangles indicate a data match. Blue circles are inconclusive. Red squares indicate a data mismatch.

Fig. 5

Scatterplots of September 1991–2020 precipitation values from GMP4 and MSWEP sources in Budapest, Hungary and St Denis, Reunion Island.

Fig. 6

(a) 2608 Stations with 50% or more GHCNd as source. (b) 974 Stations with less than 50% GHCNd as source. Green triangles, blue circles, and red squares indicate a ranked correlation in the ranges greater than or equal to 0.75, between 0.5 and 0.75, and less than 0.5, respectively.