Green hills above the northern wall,
White water winding east of the city.
On this spot our single act of parting,
The lonely tumbleweed journeys ten thousand li.
Drifting clouds echo the traveller's thoughts,
The setting sun reflects my old friend's feelings.
You wave your hand and set off from this place,
Your horse whinnies as it leaves.

Lai Bai is sad because his friend is leaving, and the tumbleweeds is a metaphor for lonliness and the setting sun is a metaphor for something ending.

the picture reminds me of the poem because of the clouds and it looked onely.