2024 Update from HadISDH.land.4.6.1.2024f

1) How does the new version compare?

v4.6.1.2024f is virtually identical to v4.6.0.2023f over the 1973-2023 period for specific humidity (q) and relative humidity (RH). Each year there is usually a small change to the source station dataset as a few stations or subperiods of stations are added or lost from processing within the source dataset (NOAA NCEI's ISD). In terms of gridboxes with sufficient presence over the climatology period, the new version v4.6.1.2024f results in 12 (for q) and 7 (for RH) lost gridboxes. There are 15 (for q) and 10 (for RH) additional gridboxes (Figs. 1 and 2 panel a). These have made negligible difference to the regional mean timeseries.

The overall story of increasing specific humidity is concurrent in both versions with v4.6.1.2024f (including its extra year of data) showing a slight increase (0.01 g kg -1 decade -1 larger) in long-term moistening trends over the Northern Hemisphere and Globe and no change over the tropics. The zero trend in the Southern Hemisphere has increased to 0.01 g kg -1 decade -1, yet is still insignificant (Figure 1 panels d to g). Across the globe (Figure 1 panel a) the vast majority of gridboxes show trends in the same direction (96%  of gridboxes - Figure 1 panel b), with 87% of these both showing increasing q (Figure 1 panel b). Trends in opposite directions occur in 4 % of gridboxes. 

The overall story of decreasing relative humidity (except over the tropics) is also still valid in both versions, but slightly weaker, with long-term negative RH trends in v4.6.1.2024f being 0.01 %rh decade -1 less negative for the Globe and Northern Hemisphere, 0.02 %rh decade -1 less negative over the tropics (still not significant), and identical over the Southern Hemisphere (Figure 2 panels d to g). Across the globe (Figure 2 panel a), 87.5% of gridboxes have trends in the same direction in both versions which is a slightly smaller proportion compared to q (Figure 1 panel b). Overall, 56.7% of gridboxes agree on negative trends and 30.8% agree on positive RH trends. 

Figure 1. Difference in regional timeseries and decadal trends between HadISDH.landq v4.6.1.2024f and v4.6.0.2023f. a) Ratio of v4.6.1.2024f to v4.6.0.2023f decadal trends (1973-2024 and 2023 respectively) with change in number of gridboxes annotated and identified by red (gained) and pink (lost). b) Scatter plot of gridbox trends with percentage in each quadrant of positive/positive, positive/negative, negative/negative and negative/positive annotated. c) Distribution of gridbox decadal trends for each version with mean and standard deviation annotated. d) Total gridbox coverage by 5 degree latitude band for each year for v4.6.1.2024f. e) Difference in total gridbox coverage by 5 degree latitude band for each year between v4.6.1.2024f and v4.6.0.2023f. f to i) regional mean monthly time series and decadal trends with 90th percentile confidence range annotated.

Figure 2. Difference in regional timeseries and decadal trends between HadISDH.landRH v4.6.1.2024f and v4.6.0.2023f. a) Ratio of v4.6.1.2024f to v4.6.0.2023f decadal trends (1973-2024 and 2023 respectively) with change in number of gridboxes annotated and identified by red (gained) and pink (lost). b) Scatter plot of gridbox trends with percentage in each quadrant of positive/positive, positive/negative, negative/negative and negative/positive annotated. c) Distribution of gridbox decadal trends for each version with mean and standard deviation annotated. d) Total gridbox coverage by 5 degree latitude band for each year for v4.6.1.2024f. e) Difference in total gridbox coverage by 5 degree latitude band for each year between v4.6.1.2024f and v4.6.0.2023f. f to i) regional mean monthly time series and decadal trends with 90th percentile confidence range annotated.

2) What's New?

We use HadISD.3.4.1.2024f  as the basis for HadISDH.land.4.6.1.2024f which includes an additional 12 months of data and any ISD level processing changes during the previous 12 months. 

All other processing steps for HadISDH.land remain identical. The new version of HadISD (3.4.1.2024f) has pulled through some historical changes to stations which are passed on to HadISDH.land resulting in 9948 compared to 9667 initial stations. The end station count is further reduced after completeness checks and homogenisation. The homogeneity adjustments differ slightly due to sensitivity to the addition and loss of stations, historical changes to stations previously included and the additional 12 months of data. 

3) Summary of changes

MAJOR CHANGES (X): 

• none

MINOR BUG FIXES AND CHANGES (Y): 

•  None

BUG FIXES AND HISTORICAL DATA UPDATES (Z): 

• 9948 compared to 9667 initial selection stations last year.
• Use of HadISD.3.4.1.2024f as the basis which includes retrospective improvements (to correct data, add or remove data sections) to the historical data in NCEI's ISD archive are ongoing. These are not documented.

4) Station Counts

Version	Initial Stations	Selected Stations	Final Stations q	Final Stations RH
v4.6.1.2024f	9667	5639	5404	5453
v4.6.0.2023f	9667	5629	5394	5446