2024 Update from HadISDH.extremes.1.2.0.2024f

1) How does the new version compare?

v1.2.0.2024f is very similar to v1.1.0.2023f over the 1973-2023 period for maximum daily wet-bulb temperature magnitude (TwX) and the number of days exceeding a local, seasonal 90th percentile of daily maximum wet-bulb temperature (TwX90p). Each year there is a small change to the dataset as a few stations or subperiods of stations are added or lost from processing within the source dataset (NOAA NCEI's ISD). This year we have changed to use the median rather than the mean when averaging the maximum daily wet-bulb temperature (TwX) over space or months, because this is more robust to outliers. In terms of gridboxes with sufficient presence over the climatology period, the new version v1.2.0.2024f results in 15 (for TwX) and 25 (for TwX90p) additional gridboxes. There are 7 (for TwX) and 11 (for TwX90p) lost gridboxes (Figs. 1 and 2 panel a). These have made very little difference to the regional mean timeseries.

The overall story of increasing magnitude of humid heat extremes continues, as measured by the median of the maximum daily wet-bulb temperature (TwX) across the globe. The additional year of data, where anomalies were strongly positive, has lead to slightly more positive trends (by 0.01 ^oC decade ^-1) over the Globe, Northern Hemisphere and Southern Hemisphere. The trend remains the same over the Tropics (Figure 1 panels f to i). Across the globe (Figure 1 panel a) the vast majority of gridboxes show trends in the same direction (96.1%  of gridboxes - Figure 1 panel b), with 83.3% of these both showing increasing TwX (Figure 1 panel b). Trends in opposite directions occur in 3.9 % of gridboxes. 

The overall story of increasing frequency of humid heat extremes is strengthened in all regions by v1.2.0.2024f compared to v1.1.0.2023f. Trends are now 0.1 to 0.34 % days decade ^-1 more positive, reflecting the record high 2024 anomalies in TwX90p. Changes to the dataset have made the largest differences in the tropics (Figure 2 panels f to i). Across the globe (Figure 2 panel a), 96.2% of gridboxes have trends in the same direction in both versions. Overall, 88.6% of gridboxes agree on positive trends and 7.6% agree on negative trends. 

Figure 1. Difference in regional timeseries and decadal trends between HadISDH.extremesTwX v1.2.0.2024f and v1.1.0.2023f. a) Ratio of v1.2.0.2024f to v1.1.0.2023f 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 v1.2.0.2024f. e) Difference in total gridbox coverage by 5 degree latitude band for each year between v1.2.0.2024f and v1.1.0.2023f. 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.extremesTwX90p v1.2.0.2024f and v1.1.0.2023f. a) Ratio of v1.2.0.2024f to v1.1.0.2023f 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 v1.2.0.2024f. e) Difference in total gridbox coverage by 5 degree latitude band for each year between v1.2.0.2024f and v1.1.0.2023f. f to i) regional mean monthly time series and decadal trends with 90th percentile confidence range annotated.

2) What's New?

The HadISDH.extremes.1.2.0.2024f contains all 12 months of 2024. It is a minor new version (Y element + 1) because the median is now used for TwX and TwN to calculate the gridbox average instead of the mean. Additional variables TwX10p, TwN90p, TX10p and TN90p have been added and the TN18 variable has now been fixed and is available once again. This error was due to a MinThreshold value not being set correctly.

All other processing steps for HadISDH.extremes 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 homogeneity assessment. The homogeneity scores 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

 

BUG FIXES AND MINOR CHANGES (Y): 

•  TwX and TwN now use median rather than mean to compute the gridbox average because it is more robust to outliers.

MINOR 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 TwX	Final Stations TwX90p
v1.2.0.2024f	9948	4865	4453	4516
v1.1.0.2023f	9667	4821	4453	4453