Fig. 3: Zonally asymmetric trends in heatwave cumulative intensity (HWI) attributable to atmospheric teleconnections (AT).
a Observed zonally asymmetric trends (observed trends minus their zonal mean) in HWI. b Estimated HWI trends by AT. c Regional observed (filled bars) and estimated (hatched bars) zonally asymmetric trends in HWI averaged over Northwestern North America (NWNA), Eastern North America (ENA), Western Europe (WE), Europe (including Western Europe and Eastern Europe), Eastern Europe (EE), South Asia-central Asia (SCA), Eastern Asia (EA), and Northeastern Asia (NEA). d Proportion (units: %) of land area (gray thin line) with the same signs between observed zonally asymmetric trend and estimated trend, and its 11-degree running average (green thick line). Probability density function (PDF; units: 1) of normalized HWI during the periods of 1979–2000 (orange dashed lines) and 2001–2022 (red solid lines) in (e) all grid cells, (f) grid cells where estimated trend is greater than 2, and (g) grid cells where estimated trend is less than -2, in mid-latitude land areas (40°–65°N). Units of HWI trend in (a–c) are K decade-1. Red (blue) hatched areas in (b) represent the areas with correct signs estimated by AT with accelerated (mitigated) HWI trends. The signs of negative observed zonally asymmetric and estimated trends (blue bars) are reversed in (c). Colored solid, half solid, and hollow circles in (c) denote the trends in AT over the corresponding regions significant at the 99%, 95%, 90% confidence levels, respectively. See methods for the specific areas of different regions. Before calculating PDF in (e–g), normalized HWI is standardized by subtracting the average and dividing the standard deviation obtained from the period of 1979–2000.
