Performance-based assessment of gross primary production (GPP) products in a typical inland river basin of northwestern China
HU Jieyuan1,2, CHANG Xiaoge1, YANG Linshan1, NING Tingting1,*()
1State Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China 2University of Chinese Academy of Sciences, Beijing 101408, China
Accurate estimation of gross primary production (GPP) is crucial for understanding terrestrial carbon cycling, yet the regional performance of existing GPP products remains insufficiently quantified. This study evaluated four widely used GPP products, i.e., the Moderate Resolution Imaging Spectroradiometer (MODIS, e.g., MOD17), Global OCO-2-based Solar-Induced Chlorophyll Fluorescence (SIF) product (GOSIF), Global Land Surface Satellite (GLASS), and Penman-Monteith-Leuning Version 2 (PML_V2), across five representative ecosystems in the Heihe River Basin (HRB), northwestern China using 18 eddy covariance (EC) sites during 2007-2022. Multi-scale validation revealed pronounced spatial and ecosystem-dependent differences. Although all products captured the general basin-scale gradient, an analysis of the spatial coefficient of variation (CV) revealed distinct differences in their ability to resolve spatial heterogeneity: PML_V2 and GLASS reasonably captured the observed spatial variability, whereas MOD17 and GOSIF tended to smooth over fine-scale details. Furthermore, a systematic compression of the productivity gradient was evident across products, characterized by considerable underestimation in high-productivity ecosystems (forest land and cropland) and general overestimation in grassland. Temporally, all products performed more reliably in capturing seasonal dynamics than in reproducing inter-annual variations. At the growing season scale, GLASS and GOSIF achieved the highest explanatory power (r>0.95 at several sites), whereas MOD17 exhibited the lowest error (root mean square error (RMSE)=25.26 g C/m2 at the Jingyangling site (JYL)). However, inter-annual performance declined markedly, with MOD17 showing weak correlations (r<0.30) at most sites. Ecosystem-specific results identified GOSIF as superior for cropland and wetland ecosystems, while PML_V2 offered the best performance in grassland and desert ecosystems by minimizing systematic bias. Notably, all products consistently failed to establish meaningful correlations (r<0.21) with observations in desert areas due to the low ratios of signal to noise. Consequently, we recommend an ecosystem-dependent application strategy—specifically prioritizing GOSIF for cropland and wetland and PML_V2 for grassland—and urge extreme caution when applying single remote-sensing GPP products in arid desert areas.
Received: 19 December 2025
Published: 31 July 2026
Methodology, data curation, software, and writing - original draft preparation: HU Jieyuan; Data curation, resources, and writing - review and editing: CHANG Xiaoge; Writing - review and editing: YANG Linshan; Conceptualization, supervision, validation, and writing - review and editing: NING Tingting. All authors approved the manuscript.
HU Jieyuan, CHANG Xiaoge, YANG Linshan, NING Tingting. Performance-based assessment of gross primary production (GPP) products in a typical inland river basin of northwestern China. Journal of Arid Land, 2026, 18(7): 1115-1134.
Fig. 1Sampling site and land use type in the Heihe River Basin (HRB). HMo, Huangmo; NTi, Nongtian; SDQ, Sidaoqiao; LDi, Luodi; HYL, Huyanglin; HHL, Hunhelin; DSL, Dashalong; ZYW, Zhangye wetland; BJT, Bajitan; DMS, super Daman; YKe, Yingke; SSW, Shenshawo; HZZ, Huazhaizi; DDS, Dadongshu; ARS, super Arou; ARo, Arou; JYL, Jingyangling; GTa, Guantan.
No.
Name
Site_ID
Longitude
Latitude
Land use type
Dominant plant
Elevation (m)
Period
Stream
1
Jingyangling site
JYL
101°06′58″E
37°50′18″N
Alpine grassland
Kobresia pygmaea (C. B. Clarke) C. B. Clarke
3750
2018-2022
Up
2
Super Arou site
ARS
100°27′51″E
38°02′50″N
Alpine grassland
K. pygmaea
3033
2013-2022
Up
3
Dadongshu site
DDS
100°14′32″E
38°00′51″N
Alpine grassland
K. pygmaea
4148
2015-2022
Up
4
Dashalong site
DSL
98°56′26″E
38°50′24″N
Alpine marshland
K. pygmaea
3739
2013-2022
Up
5
Super Daman site
DMS
100°22′20″E
38°51′20″N
Cropland
Seed corn
1556
2012-2022
Middle
6
Zhangye wetland site
ZYW
100°26′47″E
38°58′30″N
Wetland
Reed
1460
2012-2022
Middle
7
Huazhaizi site
HZZ
100°19′07″E
38°45′55″N
Desert
Salsola passerina Bunge
1731
2012-2022
Middle
8
Sidaoqiao site
SDQ
101°08′15″E
42°00′04″N
Woodland
Tamarisk
873
2013-2022
Down
9
Hunhelin site
HHL
101°08′01″E
41°59′25″N
Woodland
Populus euphratica Olivier and Tamarix L.
874
2013-2022
Down
10
Huangmo site
HMo
100°59′14″E
42°06′49″N
Desert
Reaumuria L.
1054
2015-2022
Down
11
Arou site
ARo
100°27′53″E
38°02′39″N
Alpine grassland
K. pygmaea
3033
2008-2011
Up
12
Guantan site
GTa
100°15′00″E
38°32′00″N
Subalpine forest land
Picea crassifolia Kom.
2835
2010-2011
Up
13
Yingke site
YKe
100°24′37″E
38°51′26″N
Cropland
Seed corn
1519
2008-2011
Middle
14
Bajitan site
BJT
100°18′15″E
38°54′54″N
Gobi
-
1562
2012-2014
Middle
15
Shenshawo site
SSW
100°29′36″E
38°47′21″N
Desert
-
1594
2012-2015
Middle
16
Luodi site
LDi
101°07′57″E
41°59′57″N
Bare land
-
878
2013-2015
Down
17
Nongtian site
NTi
101°08′02″E
42°00′17″N
Cropland
Cucumis melo L.
875
2013-2015
Down
18
Huyanglin site
HYL
101°07′26″E
41°59′36″N
Woodland
P. euphratica
876
2013-2015
Down
Table 1 Site information from the eddy covariance (EC) flux stations in the Heihe River Basin (HRB)
Fig. 2Statistical comparison between site-based observations and four gross primary production (GPP) products, i.e., Penman-Monteith-Leuning Version 2 (PML_V2), Moderate Resolution Imaging Spectroradiometer (MODIS, e.g., MOD17), GOSIF (Global OCO-2-based Solar-Induced Chlorophyll Fluorescence), and GLASS (Global Land Surface Satellite). (a-c), Pearson's correlation coefficient (r), root mean square error (RMSE), and bias at the growing season scale across the 18 sites, respectively; (d-f), r, RMSE, and bias at the inter-annual scale across the 11 sites with at least 5 a of continuous observations to ensure statistical robustness, respectively. The information of sampling sites is shown in Table 1.
Fig. 3Spatial pattern of growing season mean GPP derived from the products (map color) and observations (point markers). (a), GLASS; (b), GOSIF; (c), MOD17; (d), PML_V2.
Fig. 4Spatial pattern of annual mean GPP derived from the products (map color) and observations (point markers). (a), GLASS; (b), GOSIF; (c), MOD17; (d), PML_V2.
Scale
Dataset
Mean GPP (g C/m2)
Standard deviation (g C/m2)
CV (%)
Growing season
Observed
517.23
423.31
82
MOD17
359.59
241.29
67
PML_V2
378.41
331.70
88
GOSIF
440.20
304.97
69
GLASS
272.38
225.42
83
Annual
Observed
605.25
450.45
74
MOD17
400.10
260.07
65
PML_V2
447.59
374.17
84
GOSIF
465.06
315.89
68
GLASS
294.01
230.60
78
Table 2 Coefficient of variation (CV) of observed and product-derived GPP at the growing season and annual scales in the HRB
Fig. 5Monthly time series of GPP derived from observations (Obs) and products for (a) grassland, (b) cropland, (c) forest land, (d) desert, and (e) wetland ecosystems
Fig. 6Scatter plots of observed and product-derived GPP across different ecosystems. (a1-a4), grassland; (b1-b4), wetland; (c1-c4), forest land; (d1-d4), desert; (e1-e4), cropland.
Fig. 7Multi-year annual mean GPP derived from observations (Obs) and products across different ecosystems. (a), grassland; (b), cropland; (c), forest land; (d), desert; (e), wetland. Bars represent standard deviation. Negative lower bounds occur mathematically due to high spatial variance, though actual GPP values are strictly non-negative.
Fig. 8Comparison of inter-annual variability between observed and product-derived GPP across the 18 sites in the HRB. CV, coefficient of variation.
Fig. 9Response of product-derived GPP relative biases to inter-annual precipitation anomalies (Z-score) during 2007-2022 across the 18 sites in the HRB
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