Moisture anomaly conditions within humid and subhumid tropics that are associated with different types of El Niño and La Niña phenomena are described and analyzed with a focus on their spatial distribution and seasonal variability. Five dryness indices (Keetch–Byram Drought Index, Weighted Anomaly Standardized Precipitation Index, Standardized Precipitation Index, Palmer Drought Severity Index, and Percent of Normal Precipitation) were derived from ECMWF (European Centre for Medium-Range Weather Forecasts) fifth generation reanalysis (ERA5) reanalysis and University Corporation for Atmospheric Research (UCAR) datasets for the period from 1979 to 2019. Cross-correlation analysis was used to evaluate the relationships between the El Niño Southern Oscillation (ENSO) and selected dryness indices. To describe the seasonal variability of the ENSO–surface moisture relationships, the composite maps of dryness indices in different seasons were analyzed. The results showed a significant heterogeneity of the ENSO-induced moisture anomaly conditions both within and across various geographical regions. Four main areas in humid and subhumid tropics with the maximum effects of El Niño/La Niña events on the surface moisture conditions were found: Southeast Asia and Australia, Eastern and South Africa, Northeastern and Eastern South America, and Central America. It was shown that the effects of La Niña were usually opposite to those of El Niño, while the responses to the two types of El Niño differed mostly in the moisture anomaly intensity and its spatial patterns.

Forest ecosystems in the mid-latitudes of the Northern Hemisphere are significantly affected by frequent extreme weather events. How different forest ecosystems respond to these changes is a major challenge. This study aims to assess differences in the response of daily net ecosystem exchange (NEE) of CO₂ and latent heat flux (LE) between different boreal and temperate ecosystems and the atmosphere to extreme weather events (e.g., anomalous temperature and precipitation). In order to achieve the main objective of our study, we used available reanalysis data and existing information on turbulent atmospheric fluxes and meteorological parameters from the global and regional FLUXNET databases. The analysis of NEE and LE responses to high/low temperature and precipitation revealed a large diversity of flux responses in temperate and boreal forests, mainly related to forest type, geographic location, regional climate conditions, and plant species composition. During the warm and cold seasons, the extremely high temperatures usually lead to increased CO₂ release in all forest types, with the largest response in coniferous forests. The decreasing air temperatures that occur during the warm season mostly lead to higher CO₂ uptake, indicating more favorable conditions for photosynthesis at relatively low summer temperatures. The extremely low temperatures in the cold season are not accompanied by significant NEE anomalies. The response of LE to temperature variations does not change significantly throughout the year, with higher temperatures leading to LE increases and lower temperatures leading to LE reductions. The immediate response to heavy precipitation is an increase in CO₂ release and a decrease in evaporation. The cumulative effect of heavy precipitations is opposite to the immediate effect in the warm season and results in increased CO₂ uptake due to intensified photosynthesis in living plants under sufficient soil moisture conditions.

The heat budget of the equatorial Pacific mixed layer during El Niño formation was studied based on reanalysis (GLORYS2V4) and model data for the modern climate. The focus of the study is on the so-called El Niño diversity, i.e., the existence of different types of events that are characterized by different locations and intensities, as well as significantly different teleconnection all around the world. The analysis of the processes that participate in the formation of different El Niño types may serve for a better understanding of the El Niño dynamic and contribute to improving its forecast. Two classifications, based on the location and intensity of the events, were considered: strong/moderate and Eastern Pacific (EP)/Central Pacific (CP). The analysis did not reveal a significant difference in the heat budget of the mixed layer between strong and EP El Niño events, as well as between moderate and CP events. The major difference in the generation mechanism of strong (EP) and moderate (CP) El Niño events consists of the magnitude of heating produced by ocean heat budget components with higher heating rates for strong (EP) events. The evolution of sea surface temperature anomalies (SSTA) is governed primarily by oceanic advection. The vertical advection (due to the thermocline feedback) is the main contributor to SSTA growth in the eastern Pacific regardless of El Niño’s type. In the Central Pacific, horizontal advection is more important than vertical one, with a stronger impact of meridional processes for both strong and moderate regimes. Furthermore, the evaluation of the CMIP5 model’s skill in the simulation of the processes responsible for the formation of different El Niño types was carried out. The analysis of the heat budget of the mixed layer in the CMIP5 ensemble demonstrated that the most successful models are CCSM4, CESM1-BGC, CMCC-CMS, CNRM-CM5, GFDL-ESM2M, and IPSL-CM5B-LR. They are capable of reproducing the most important contribution of the advection terms in the SSTA tendency, keeping the major role of the thermocline feedback (and vertical advection) in the eastern Pacific, and do not overestimate the contribution of zonal advective feedback. These models are recommended to be used for the analysis of El Niño mechanism modification in the future climate.

This study conducted a comprehensive assessment of the response of wetland ecosystems in temperate and polar latitudes, located on different continents, to extreme weather events. These events included temperature anomalies (unusually high/low temperatures) and precipitation anomalies (droughts/intense precipitation). The analysis of the response net ecosystem exchange (NEE) of CO2 and latent heat (LE) fluxes to extreme temperature and precipitation events used ERA5 reanalysis data [Smith, 2011] and observations of CO2 and LE fluxes from the global FLUXNET database [https://fluxnet.org/data/]. Fifteen greenhouse gas flux monitoring stations were selected for the study, representing the longest and most continuous time series of observations. These stations are located on different continents, with eight stations in temperate latitudes and seven in polar regions. It should be noted that this study focused exclusively on the warm season. The beginning and end of the warm season were defined as the sustained crossing of the daily mean air temperature above 0°C for at least seven consecutive days. For each station, daily anomalies of CO2 and LE fluxes were calculated as the deviation from the long-term mean values for the corresponding day of the year. Extremely high/low values of flux anomalies were identified as exceeding one standard deviation from the overall time series for each calendar month individually. To identify periods with extreme air temperature values, ERA5 reanalysis data on two-meter air temperature every 3 hours with a spatial resolution of 0.25°×0.25° from 1991 to 2021 were used. To estimate extreme precipitation amounts, data from half-hourly station observations were used. Daily means were calculated from these data in a first step. Thresholds for defining extremely hot/cold periods were calculated as daily mean air temperature exceeding the 95th percentile (for anomalously hot periods) or not exceeding the 5th percentile (for anomalously cold periods) of a normal distribution with mean and standard deviation. The distribution was constructed for a specific month of the year and then averaged over the entire period considered. Two approaches were used to determine the extreme precipitation threshold. In the first approach, extreme precipitation days were defined as days with daily precipitation exceeding the 95th percentile of the probability density function (the Weibull distribution was used for precipitation). The second approach was based on the assessment of the Antecedent Precipitation Index (API), which determines the cumulative effect of precipitation on CO2 fluxes. For the quantitative assessment of the relationship between temperature and precipitation extremes and flux anomalies, the percentages of days on which both the NEE/LE anomaly exceeded the standard deviation and the temperature/precipitation exceeded the 95th percentile for the upper threshold or the temperature did not reach the 5th percentile for the lower threshold were calculated. The percentage was calculated based on the total number of days when one of the characteristics (air temperature, daily sum of precipitation) exceeded the threshold. The analysis showed that temperate and polar wetland ecosystems can respond differently to temperature and precipitation anomalies. These differences can be attributed to the geographic location of the ecosystem, regional climatic conditions, plant species composition, and the intensity of temperature and precipitation extremes. During the warm half of the year, periods of extremely high temperatures in temperate latitudes were associated with a positive CO2 flux anomaly, corresponding to an increased emission of CO2 into the atmosphere. In contrast, polar latitudes showed an opposite response - an increase in CO2 uptake by wetland ecosystems under anomalously high temperatures. This opposite response of CO2 fluxes may be related to the different soil moisture regimes in polar wetland ecosystems and the different plant species composition. Extremely high temperatures were accompanied by positive LE anomalies due to the intensification of evaporation processes with rising temperatures, a trend observed in all wetland ecosystems analyzed. The immediate response of wetland ecosystems to intense precipitation (above the 95th percentile) was manifested as an increase in CO2 flux to the atmosphere at almost all stations analyzed. This observed response could be related to the "Birch effect" [Birch, 1964], which is characterized by an intensification of soil respiration due to a sudden increase in soil moisture and, consequently, an increase in the rate of decomposition and mineralization of organic matter during heavy precipitation and rising groundwater levels. LE flux decreases during intense precipitation, indicating suppression of evaporation due to high humidity and reduced incoming solar radiation. The cumulative effect (API index) of extremely high precipitation is characterized by a predominance of extremely positive CO2 flux anomalies over negative ones in wetland ecosystems at both temperate and polar latitudes. It should also be noted that the percentage of days with increased CO2 uptake during the two weeks following intense precipitation is significantly higher than for the immediate response (10-25% of days in temperate latitudes and 5-20% of days in polar latitudes). The increase in CO2 uptake after heavy precipitation may be related to enhanced photosynthetic rates of the vegetation cover under sunny weather and optimal soil moisture conditions. A prolonged absence of precipitation, represented by extremely low API values, is accompanied by negative CO2 flux anomalies (enhanced uptake) at most of the studied wetland ecosystem stations, indicating a high adaptive potential of the studied wetland ecosystems to short-term (less than 14 days) dry periods. On the other hand, enhanced CO2 uptake could be facilitated by clear...